zebra: Fix neighbor update to BGP

zebra: Fix neighbor update to BGP

Ensure that when the is_router condition changes for a locally learnt
neighbor, it is informed to BGP only if it is active i.e., the MAC is
also locally learnt.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Anuradha Karuppiah <anuradhak@cumulusnetworks.com>
Reviewed-by:   Chirag Shah <chirag@cumulusnetworks.com>
Ticket: CM-22288
Reviewed By: CCR-7832
Testing Done:
1. Failed test
2. vxlan_routing_test.py