Zebra: Fix neighbor address notification to clients

Zebra: Fix neighbor address notification to clients

This problem was fixed as part of implementation of VRF change semantics
for an interface, though it is not directly related. The issue here
was that neighbor addresses learnt on an interface were being informed
to clients even though the clients may not have learnt of the interface.
Fixed by introducing the correct checks.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by:   Don Slice <dslice@cumulusnetworks.com>
Ticket: CM-9527
Reviewed By: CCR-4174
Testing Done: Manual tests of various scenarios