D-Bus NetworkManager improvements (#3243)

* Introduce enum for network connectivity

* Differentiate between Bus Name and Interface consts

The Bus names and interfaces look quite similar in D-Bus: Both use dots
to separate words. Usually all interfaces available below a certan Bus
name start with the Bus name. Quite often the Bus name itself is also
available as an interface.

However, those are different things. To avoid confusion, add the type of
const to the const name.

* Remove unused const

* Disconnect D-Bus when not used

Make sure Python disconnects from D-Bus when objects get destroyed. This
avoids exhausting D-Bus connection limit which causes the following
error message:
[system] The maximum number of active connections for UID 0 has been reached (max_connections_per_user=256)

* Filter signals by object as well

Make sure we only listen to signals on that particular object. Also
support filtering messages via message filter callback.

* Explicitly wait until Connection is activated

Wait for activated or raise an error. This avoids too early/errornous
updates when state of the connection changes to "activating" or similar
intermediate signal states.

Fixes: #2639

* Fix VLAN configuration

* Add link to D-Bus object documentation

* Fix network settings update test

* Make MessageBus object optional

tests/conftest.py

@@ -18,6 +18,7 @@ from supervisor.api import RestAPI
 from supervisor.bootstrap import initialize_coresys
 from supervisor.const import REQUEST_FROM
 from supervisor.coresys import CoreSys
+from supervisor.dbus.const import DBUS_SIGNAL_NM_CONNECTION_ACTIVE_CHANGED
 from supervisor.dbus.network import NetworkManager
 from supervisor.docker import DockerAPI
 from supervisor.store.addon import AddonStore
@@ -79,8 +80,9 @@ def dbus() -> DBus:
 
         return load_json_fixture(f"{fixture}.json")
 
-    async def mock_wait_signal(_, __):
-        pass
+    async def mock_wait_signal(_, signal_method, ___):
+        if signal_method == DBUS_SIGNAL_NM_CONNECTION_ACTIVE_CHANGED:
+            return [2, 0]
 
     async def mock_init_proxy(self):