zebra:remote vtep delete handling

zebra:remote vtep delete handling

The existing behavior is when a remote VTEP is deleted,
its associatedneighbor (arp) and MAC entries are removed from
zebra database and do not wait for explicit type-2 route
withdraw from originating VTEP.
Remote type-2 route delete checks if VTEP is present before
removing the entry.
The behavior works fine when all evpn routes points to the
same nexthop as the VTEP IP.

In MLAG topology with advertise-pip, self type-2 and type-5 routes
are advertised with individual VTEP IP as nexthop ip for the route.

When a new VNI is created, it is assigned individual IP as tunnel-ip
then it transition to anycast IP (of the MLAG). During the transition,
type-3 route (VTEP delete) withdraw is sent for the individual IP.
The remote VTEP delete should not trigger to remove evpn routes pointing
to VTEP IP. Instead the route will be removed via explicit withdraw.

Ticket:CM-27752
Reviewed By:CCR-9722
Testing Done:

In evpn with MLAG deployment with advertise-pip and advertise-svi-ip
enabled, validated remote vtep delete does not remove self type-2 routes
from zebra DB. Upon explicit type-2 withdraw routes are removed.

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>