https://bugzilla.redhat.com/show_bug.cgi?id=1487322

In ace45e67abbd I've tried to fix a problem that we get the reply
to a D-Bus call while we were sleeping. In that case the callback
was never set. So I've changed the code that the callback is
called directly in this case. However, I hadn't realized that
since callback is called out of order it lock the virNetDaemon.
Exactly the very same virNetDaemon that we are dealing with right
now and have it locked already (in
virNetDaemonAddShutdownInhibition())

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>