afsocket: Warn & auto-migrate when using /dev/log under systemd

We were emitting a warning when /dev/log was in use, yet, we were
running under systemd, but only when the config version was older than
3.4. Due to various circumstances, lets extend that so it warns on 3.5
too.

Requested-by: Peter Czanik <czanik@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@balabit.hu>