zebra: act on kernel notifications for remote neighbors as well

zebra: act on kernel notifications for remote neighbors as well

There can be a race condition between kernel and frr as follows.
Frr sends remote neigh notification.
At the (almost) same time kernel might send a notification saying
neigh is local.
After processing this notifications, the state in frr is local while
state in kernel is remote. This causes kernel and frr to be out of sync.
This problem will be avoided if FRR acts on the kernel notifications for
remote neighbors. When FRR sees a remote neighbor notification for a
neighbor which it thinks is local, FRR will change the neigh state to remote.

Ticket: CM-19923/CM-18830
Review: CCR-7222
Testing: Manual

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>