As NM_SETTING_SECRET_FLAGS_ALL is used in libnm/nm-vpn-plugin-utils.c,
it is exposed as internal API and should be declared in
nm-core-internal.h.

Signed-off-by: Thomas Haller <thaller@redhat.com>

Add a header file to expose private utility functions from libnm-core
that can be used by NetworkManager (core) and libnm.so. The header
is also used to give privileged access to libnm-core. Since NM links
statically, these functions are not exported and not part of public ABI.

This also removes the NM_UTILS_PRIVATE_CALL() macro and libnm.so no
longer exports nm_utils_get_private().

Before, this functionality was partly declared in nm-utils-private.h.
This was wrong because nm-utils-private.h is for functionality
entirely private to libnm-core.

Signed-off-by: Thomas Haller <thaller@redhat.com>

Several nm-device-*.c files apparently originally used
nm-device-ethernet.c as a template, but missed a reference to "eth" in
class_init.

The fact that NMRemoteConnection has to be an NMConnection and
therefore can't be an NMObject means that it needs to reimplement bits
of NMObject functionality (and likewise NMObject needs some special
magic to deal with it). Likewise, we will need a daemon-side
equivalent of NMObject as part of the gdbus port, and we would want
NMSettingsConnection to be able to inherit from this as well.

Solve this problem by making NMConnection into an interface, and
having NMRemoteConnection and NMSettingsConnection implement it. (We
use some hacks to keep the GHashTable of NMSettings objects inside
nm-connection.c rather than having to be implemented by the
implementations.)

Since NMConnection is no longer an instantiable type, this adds
NMSimpleConnection to replace the various non-D-Bus-based uses of
NMConnection throughout the code. nm_connection_new() becomes
nm_simple_connection_new(), nm_connection_new_from_hash() becomes
nm_simple_connection_new_from_hash(), and nm_connection_duplicate()
becomes nm_simple_connection_new_clone().

NMRemoteConnection had two DBusGConnection properties
(NMRemoteConnection:bus and NMRemoteConnection:dbus-connection) and
two D-Bus path properties (NMConnection:path and
NMRemoteConnection:dbus-path). The former of each pair were the
traditional names, and the latter were added for compatibility with
NMObject.

In libnm, we can just drop NMRemoteConnection:bus, and use the
NMObject-compatible :dbus-connection name instead.

For the path properties, we need to rename either NMConnection:path or
NMObject:dbus-path. Since NMObject already has "nm_object_get_path()"
rather than "nm_object_get_dbus_path()", and it already mistakenly
referred to the property as "NMObject:path" in the gtk-docs, it seemed
to make sense to rename that one rather than the NMConnection one.

(And then, for consistency, rename "nm_object_get_connection()" to
"nm_object_get_dbus_connection()" to also match its property.)

nm_connection_lookup_setting_type() and
nm_connection_lookup_setting_type_by_quark() have nothing to do with
NMConnection. So move them to NMSetting (and rename them to
nm_setting_lookup_type() and nm_setting_lookup_type_by_quark()).

This was only used in one place, and is trivial to implement inline
there.

Previously, src/nm-ip4-config.h, libnm/nm-ip4-config.h, and
libnm-glib/nm-ip4-config.h all used "NM_IP4_CONFIG_H" as an include
guard, which meant that nm-test-utils.h could not tell which of them
was being included (and so, eg, if you tried to include
nm-ip4-config.h in a libnm test, it would fail to compile because
nm-test-utils.h was referring to symbols in src/nm-ip4-config.h).

Fix this by changing the include guards in the non-API-stable parts of
the tree:

  - libnm-glib/nm-ip4-config.h remains   NM_IP4_CONFIG_H
  - libnm/nm-ip4-config.h now uses     __NM_IP4_CONFIG_H__
  - src/nm-ip4-config.h now uses       __NETWORKMANAGER_IP4_CONFIG_H__

And likewise for all other headers.

The two non-"nm"-prefixed headers, libnm/NetworkManager.h and
src/NetworkManagerUtils.h are now __NETWORKMANAGER_H__ and
__NETWORKMANAGER_UTILS_H__ respectively, which, while not entirely
consistent with the general scheme, do still mostly make sense in
isolation.

Since NMRemoteSettings doesn't announce new connections until it has
fetched their properties, it's possible that a connection could get
deleted while we're waiting for it to be created. NMRemoteSettings has
code to deal with this, so add a test to make sure that it works.