system-source: add systemd source, if it is currently used (running as PID 1)
  on the system.

Signed-off-by: Tibor Benke <ihrwein@gmail.com>
afsocket: Auto change from unix-dgram to systemd source, when the
 socket name is "/dev/log"

Signed-off-by: Tibor Benke <ihrwein@gmail.com>