This is intended to unbreak LXD by default.

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1112

In systemd, it's common that a D-Bus activatable service references
`SystemdService=dbus-$BUSNAME.service` instead the real service name.
Together with an `[Install].Alias=dbus-$BUSNAME.service` directive,
this allowed to enable/disable D-Bus activation without uninstalling the
service altogether ([1]).

Currently, when we install the RPM then `nm-priv-helper.service` is not
enabled, consequently the alias is not created, and D-Bus activation
does not work. I guess, we should fix that by enabling the service in
the %post section or via a systemd preset? Dunno.

Anyway. It seems that nm-priv-helper.service is more of an
implementation detail of NetworkManager. It makes not sense for the user
to interact directly, or to enable/disable D-Bus activation (because
that is how it works).

So, drop the alias.

See-also: [1] https://docs.fedoraproject.org/en-US/packaging-guidelines/Systemd/#activation_dbus

"-" is not allowed as D-Bus path and interface name, and discouraged as
bus name. This cause nm-priv-helper to crash, because GDBus asserts the
the object path is valid.

Replace the '-' with '_'. This way, it's consistent with
"nm_dispatcher".

Fixes: d68ab6b8f02a ('nm-sudo: rename to nm-priv-helper')

The name "nm-sudo" reminds of the "sudo" tool, and this is a bit
confusing because it's not related. Rename the service to
"nm-priv-helper", which stands for "NM privileged helper".

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/938
(cherry picked from commit d68ab6b8f02a8de68ce6bb1207cfba4e995fd756)

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/938#note_1163013
(cherry picked from commit 5e0764cf8e7b3cdc1a8bd5b088b3ea95c394f106)

NetworkManager handles "add" and "move" actions the same way, by
tracking the "struct udev_device" instance.

Still, this means that also for move events, we need the right
attributes set.

See-also: https://github.com/openshift/sriov-network-operator/issues/414

The advantage of environment variables is that the user can use
`systemctl edit NetworkManager-dispatcher.service` for setting them,
without need to change the ExecStart= line.

Also, enabling debugging from the start is useful, despite that debug
logging can be enabled per-request.

Also, there is a difference whether we want verbose logging or whether
we want to log to stdout. There should be a flag, that only increases the
logging verbosity, but does not change the logging backend.

- exit-on-idle needs to be done correctly. Fix the race, by first
  notifying systemd (STOPPING=1), releasing the name, and all the
  while continue processing requests.

- don't use g_bus_own_name_on_connection(). That one also listens
  to NameLost and NameAcquired signals, but we don't care about those.
  systemd will take care to only spawn one process at a time. And
  anyway, the well-known name is only important to be reachable, we
  don't require it to be functional. We can get the first request
  before RequestName completed and we can continue getting requests
  after releasing the name.

nm-sudo is D-Bus activated and exits-on-idle. To do that race-free we
need:

  - sd_notify("STOPPING=1")
  - ReleaseName
  - keep processing pending requests