Now nm_shutdown_wait_obj_*() supports two styles:

 - NM_SHUTDOWN_WAIT_TYPE_OBJECT: this just registers a weak pointer
   on a source GObject. As long as the object is not destroyed
   (and the object is not unregistered), the shutdown gets blocked.

 - now new is NM_SHUTDOWN_WAIT_TYPE_CANCELLABLE: this source object
   is a GCancellable, and during shutdown, the system will cancel
   the instances to notify about the shutdown. That aside, the GCancellable
   is tracked exactly like a regular NM_SHUTDOWN_WAIT_TYPE_OBJECT (meaning:
   a weak pointer is registered and shutdown gets delayed as long as the instance
   lives).

As the rest of the shutdown, it's not yet implemented on the shutdown-side.
What is now possible is to register such cancellables, so that users can make
use of this API before we fix shutdown. We cannot fix it all at the same time,
so first users must be ready for this approach.

  $ find * -type f |xargs perl contrib/scripts/spdx.pl
  $ git rm contrib/scripts/spdx.pl

WireGuard's wq-quick configures such rules to avoid routing loops.
While we currently don't have an automatic solution for this, at least
we should support it via explicit user configuration.

One problem is that suppress_prefixlength is relatively new and kernel
might not support this attribute. That can lead to odd results, because
the NetworkManager is valid but it cannot be configured on the current
kernel. But this is a general problem, and we would require a general
solution. The solution cannot be to only support rule attributes that
are supported by the oldest possible kernel. It's not clear how much of
a problem there really is, or which general solution is required (if
any).

In fact, nm_shutdown_wait_obj_register*() API is still not implemented
and registering an object has no effect currently. That is, blocking
shutdown and waiting for instances to be destroyed during shutdown
is not yet implemented. Still, we already implement the API so that
components can register themself to block the shutdown. The point is
of course, that the callers already use this API, although it's not yet
implemented.

Anyway, sometimes the message string is not static. Add an option to
pass an allocated string and let the string be destroyed when no longer
needed.

Add a new ipv6.method value 'disabled' that completely disables IPv6
for the interface.

https://bugzilla.redhat.com/show_bug.cgi?id=1643841

We no longer add these. If you use Emacs, configure it yourself.

Also, due to our "smart-tab" usage the editor anyway does a subpar
job handling our tabs. However, on the upside every user can choose
whatever tab-width he/she prefers. If "smart-tabs" are used properly
(like we do), every tab-width will work.

No manual changes, just ran commands:

    F=($(git grep -l -e '-\*-'))
    sed '1 { /\/\* *-\*-  *[mM]ode.*\*\/$/d }'     -i "${F[@]}"
    sed '1,4 { /^\(#\|--\|dnl\) *-\*- [mM]ode/d }' -i "${F[@]}"

Check remaining lines with:

    git grep -e '-\*-'

The ultimate purpose of this is to cleanup our files and eventually use
SPDX license identifiers. For that, first get rid of the boilerplate lines.

It's a common thing to complete a connection with an interface name;
adding it to the common path is goint to save as a few tens of lines
later on.

"libnm-core" implements common functionality for "NetworkManager" and
"libnm".

Note that clients like "nmcli" cannot access the internal API provided
by "libnm-core". So, if nmcli wants to do something that is also done by
"libnm-core", , "libnm", or "NetworkManager", the code would have to be
duplicated.

Instead, such code can be in "libnm-libnm-core-{intern|aux}.la".
Note that:

  0) "libnm-libnm-core-intern.la" is used by libnm-core itsself.
     On the other hand, "libnm-libnm-core-aux.la" is not used by
     libnm-core, but provides utilities on top of it.

  1) they both extend "libnm-core" with utlities that are not public
     API of libnm itself. Maybe part of the code should one day become
     public API of libnm. On the other hand, this is code for which
     we may not want to commit to a stable interface or which we
     don't want to provide as part of the API.

  2) "libnm-libnm-core-intern.la" is statically linked by "libnm-core"
     and thus directly available to "libnm" and "NetworkManager".
     On the other hand, "libnm-libnm-core-aux.la" may be used by "libnm"
     and "NetworkManager".
     Both libraries may be statically linked by libnm clients (like
     nmcli).

  3) it must only use glib, libnm-glib-aux.la, and the public API
     of libnm-core.
     This is important: it must not use "libnm-core/nm-core-internal.h"
     nor "libnm-core/nm-utils-private.h" so the static library is usable
     by nmcli which couldn't access these.

Note that "shared/nm-meta-setting.c" is an entirely different case,
because it behaves differently depending on whether linking against
"libnm-core" or the client programs. As such, this file must be compiled
twice.

(cherry picked from commit af07ed01c04867e281cc3982a7ab0d244d4f8e2e)

From the files under "shared/nm-utils" we build an internal library
that provides glib-based helper utilities.

Move the files of that basic library to a new subdirectory
"shared/nm-glib-aux" and rename the helper library "libnm-core-base.la"
to "libnm-glib-aux.la".

Reasons:

 - the name "utils" is overused in our code-base. Everything's an
   "utils". Give this thing a more distinct name.

 - there were additional files under "shared/nm-utils", which are not
   part of this internal library "libnm-utils-base.la". All the files
   that are part of this library should be together in the same
   directory, but files that are not, should not be there.

 - the new name should better convey what this library is and what is isn't:
   it's a set of utilities and helper functions that extend glib with
   funcitonality that we commonly need.

There are still some files left under "shared/nm-utils". They have less
a unifying propose to be in their own directory, so I leave them there
for now. But at least they are separate from "shared/nm-glib-aux",
which has a very clear purpose.

(cherry picked from commit 80db06f768e47541eae7d66ef48fbe47bf1a69ce)