It is now unused.

https://bugzilla.gnome.org/show_bug.cgi?id=790061

We need to pass more alias-types. Instead of having numbered
versions, use variadic number of macro arguments.

Also, fix build failure with old compiler:

  In file included from src/nm-ip6-config.c:24:
  ./src/nm-ip6-config.h:44:29: error: controlling expression type 'typeof (ipconf_iter->current->obj)' (aka 'const void *const') not compatible with any generic association type
                  *out_address = has_next ? NMP_OBJECT_CAST_IP6_ADDRESS (ipconf_iter->current->obj) : NULL;
                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: b1810d7a68d188aa8f36a0e23a7be705a742b1aa

_NM_GET_PRIVATE() used typeof() to propagate constness of the @self
pointer. However, that means, it could only be used with a self pointer
of the exact type. That means, you explicitly had to cast from (GObject *)
or from (void *).
The requirement is cumbersome, and often led us to either create @self
pointer we didn't need:

    NMDeviceVlan *self = NM_DEVICE_VLAN (device);
    NMDeviceVlanPrivate *priv = NM_DEVICE_VLAN_GET_PRIVATE (self);

or casting:

    NMDeviceVlanPrivate *priv = NM_DEVICE_VLAN_GET_PRIVATE ((NMDevice *) device);

In both cases we forcefully cast the source variable, loosing help from
the compiler to detect a bug.

For "nm-linux-platform.c", instead we commonly have a pointer of type
NMPlatform. Hence, we always forcefully cast the type via _NM_GET_PRIVATE_VOID().

Rework the macro to use _Generic(). If compiler supports _Generic(), then we
will get all compile time checks as desired. If the compiler doesn't support
_Generic(), it will still work. You don't get the compile-time checking of course,
but you'd notice that something is wrong once you build with a suitable
compiler.

Kernel does not allow setting the MTU of a VLAN larger
then the MTU of the underlying device. Hence, we might
initially fail to set a large MTU of the VLAN, but we
have to retry when the MTU of the parent changes.

https://bugzilla.redhat.com/show_bug.cgi?id=1414901

The message should only tell what went wrong.

At startup the manager tries to create virtual devices without a
specific order and spits warnings when a device can't be realized
because the parent device is not yet created. These failures are not
something the user should worry about because the creation will be
retried when the parent appears.

A better approach is to return an error code from the device's
create_and_realize() telling that it failed because the parent doesn't
exist. In this way, the manager knows that the device isn't ready and
can avoid printing warning messages.

Change the output of nm_platform_error_to_string() to print the numeric value.
Also, accept a string buffer instead of using an alloca() allocated buffer.

There is still a macro to provide the previous functionality, but it
was ill-suited to call from inside a loop.

do a check on parent ifindex before calling "nm_device_supports_vlans"
otherwise if the parent device is a software device and its ifindex
member has not been updated yet we will trigger the g_return_if_fail
statement in "nmp_cache_lookup_entry_link".

This has been osserved in NetworkManager CI test suite, on NetworkManager
boot, during the creation of a vlan on top of a bond interface.

CI test: vlan_update_mac_from_bond

    [...]
    <info>  [1503323670.0229] manager: (bond0): new Bond device (/org/freedesktop/NetworkManager/Devices/23)
    <debug> [1503323670.0231] device[0x555555c3e320] (vlan10): constructed (NMDeviceVlan)
    <debug> [1503323670.0231] manager: (vlan-vlan10) create virtual device vlan10
    <debug> [1503323670.0231] device[0x555555c3e320] (vlan10): unmanaged: flags set to [platform-init,!sleeping=0x10/0x11/unmanaged/unrealized], set-managed [sleeping=0x1])
    <trace> [1503323670.0235] exported-object[0x555555c3e320]: export: "/org/freedesktop/NetworkManager/Devices/24"
    <trace> [1503323670.0235] properties-changed[0x555555c3e320]: ignoring notification for prop g-object-path on type NMDeviceVlan
    <trace> [1503323670.0236] properties-changed[0x555555c3e320]: ignoring notification for prop path on type NMDeviceVlan
    <info>  [1503323670.0237] manager: (vlan10): new VLAN device (/org/freedesktop/NetworkManager/Devices/24)
    <debug> [1503323670.0239] device[0x555555c3e320] (vlan10): create (is nm-owned)

    Program received signal SIGTRAP, Trace/breakpoint trap.
    g_logv (log_domain=0x5555557c39a9 "NetworkManager", log_level=
        G_LOG_LEVEL_CRITICAL, format=<optimized out>,
        args=args@entry=0x7fffffffdef0) at gmessages.c:1086
    1086		  g_private_set (&g_log_depth, GUINT_TO_POINTER (depth));

    (gdb) bt

    #0  0x00007ffff5ce3643 in g_logv (log_domain=0x5555557c39a9 "NetworkManager", log_level=
        G_LOG_LEVEL_CRITICAL, format=<optimized out>, args=args@entry=0x7fffffffdef0) at gmessages.c:1086
    #1  0x00007ffff5ce37bf in g_log (log_domain=log_domain@entry=0x5555557c39a9 "NetworkManager", log_level=log_level@entry=G_LOG_LEVEL_CRITICAL, format=format@entry=0x7ffff5d51190 "%s: assertion '%s' failed") at gmessages.c:1119
    #2  0x00007ffff5ce37f9 in g_return_if_fail_warning (log_domain=log_domain@entry=0x5555557c39a9 "NetworkManager", pretty_function=pretty_function@entry=0x5555557b2a20 <__func__.32407> "nmp_cache_lookup_entry_link", expression=expression@entry=0x5555557b1037 "ifindex > 0") at gmessages.c:1128
    #3  0x000055555566688a in nmp_cache_lookup_entry_link (cache=0x555555a780f0, ifindex=<optimized out>) at src/platform/nmp-object.c:1449
    #4  0x00005555556668f9 in nmp_cache_lookup_link (cache=<optimized out>, ifindex=ifindex@entry=0) at src/platform/nmp-object.c:1464
    #5  0x00005555556515e9 in nm_platform_link_get_obj (self=self@entry=0x555555a88880 [NMLinuxPlatform], ifindex=ifindex@entry=0, visible_only=visible_only@entry=1) at src/platform/nm-platform.c:618
    #6  0x0000555555633e91 in link_supports_vlans (platform=0x555555a88880 [NMLinuxPlatform], ifindex=0) at src/platform/nm-linux-platform.c:4482
    #7  0x00005555556d6d41 in create_and_realize (device=0x555555c3e320 [NMDeviceVlan], connection=0x7fffdc007890, parent=0x555555c33560 [NMDeviceBond], out_plink=0x7fffffffe1f8, error=0x7fffffffe358) at src/devices/nm-device-vlan.c:239
    #8  0x00005555556b934c in nm_device_create_and_realize (self=self@entry=0x555555c3e320 [NMDeviceVlan], connection=connection@entry=0x7fffdc007890, parent=0x555555c33560 [NMDeviceBond], error=error@entry=0x7fffffffe358)
        at src/devices/nm-device.c:2946
    #9  0x00005555555b84c7 in connection_changed (connection=0x7fffdc007890, self=0x555555ab1070 [NMManager]) at src/nm-manager.c:1381
    #10 0x00005555555b84c7 in connection_changed (self=0x555555ab1070 [NMManager], connection=0x7fffdc007890) at src/nm-manager.c:1431
    #11 0x00005555555b9130 in retry_connections_for_parent_device (self=self@entry=0x555555ab1070 [NMManager], device=device@entry=0x555555c33560 [NMDeviceBond])
        at src/nm-manager.c:1416
    #12 0x00005555555b95c7 in add_device (self=self@entry=0x555555ab1070 [NMManager], device=device@entry=0x555555c33560 [NMDeviceBond], error=error@entry=0x7fffffffe598) at src/nm-manager.c:2238
    #13 0x00005555555b83e1 in connection_changed (connection=0x7fffdc007b30, self=0x555555ab1070 [NMManager]) at src/nm-manager.c:1352
    #14 0x00005555555b83e1 in connection_changed (self=0x555555ab1070 [NMManager], connection=0x7fffdc007b30) at src/nm-manager.c:1431
    #15 0x00005555555be25b in nm_manager_start (self=0x555555ab1070 [NMManager], error=error@entry=0x7fffffffe720) at src/nm-manager.c:5202
    #16 0x0000555555586b13 in main (argc=1, argv=0x7fffffffe888) at src/main.c:413