bgpd: on ES down re-advertise the MAC-IP entry without the L3 ECOM

bgpd: on ES down re-advertise the MAC-IP entry without the L3 ECOM

When an ES goes down the MAC-IP route must be updated to remove it from
the tenant VRF routing table. This is because the fast-failover
(via EAD-per-ES withdraw) procedures described in RFC 7432 are only
applicable to L2 forwarding/MAC-ECMP. For L3/routed traffic (in a
sym-IRB setup) failover, individual paths need to be withdrawn.

To handle this difference in L2/L3 requirements BGP updates the MAC-IP
route to include the L3 ECOM if local destination ES is oper-up and
to exclude the L3 ECOM if local ES is oper-down.

Ticket: CM-30935

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>