nwfilter: grab driver lock earlier during init (bz96649)

nwfilter: grab driver lock earlier during init (bz96649)

This patch is in relation to Bug 966449:

https://bugzilla.redhat.com/show_bug.cgi?id=966449

This is a patch addressing the coredump.

Thread 1 must be calling  nwfilterDriverRemoveDBusMatches(). It does so with
nwfilterDriverLock held. In the patch below I am now moving the
nwfilterDriverLock(driverState) further up so that the initialization, which
seems to either take a long time or is entirely stuck, occurs with the lock
held and the shutdown cannot occur at the same time.

Remove the lock in virNWFilterDriverIsWatchingFirewallD to avoid
double-locking.

(cherry picked from commit 0ec376c20a42b9eb365c1f9a5596366023c20c35)