ospfd: fix invocation of ospfTrapNbrStateChange

ospfd: fix invocation of ospfTrapNbrStateChange

ospfNbrStateChange is generated when the state of neighbor regresses or
it progresses to a terminal state. When transitioning to or from Full
state on non-broadcast multi-access and broadcast networks the trap
should be sent by the designated router. This last condition was not
taken into account when checking for the conditions of generating the
trap.

Fixes volta/volta-stack#1811

Signed-off-by: Babis Chalios <mail@bchalios.io>