zebra: Fix MAC change handling for a neighbor

zebra: Fix MAC change handling for a neighbor

When the MAC changes for a local neighbor, ensure that the neighbor data
structure as well as the link between the neighbor and MAC data structures
is updated correctly.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Mitesh Kanjariya <mitesh@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Ticket: CM-17565
Reviewed By: CCR-6605
Testing Done: Manual, evpn-smoke