Faster sync group transition

Suggestion to speed up sync group transitions.

Send prio 0 when entering FAULT state:
This fix will send prio 0 (VRRP_PRIO_STOP) when the VRRP router transists from MASTER to FAULT state. This will make a sync group leave the MASTER state more quickly by notifying the backup router(s) instead of having them to wait for time out.

Quick sync group transition:
In a sync group, when waiting for all instances to want master state, this fix will check the instances for transition every advert interval instead of every third. This will make a sync group transition occur more quickly.