zebra: prevent crash in evpn if cleanup

zebra: prevent crash in evpn if cleanup

zebra crash is seen while cleaning up evpn interface
during shutdown event.
evpn interface clean up is called from vrf_delete callback

(gdb) frame 4
(is_up=false, br_zif=0x0, vlan_zif=0x557f31fb36f0) at zebra/zebra_evpn_mh.c:614
614     zebra/zebra_evpn_mh.c: No such file or directory.
(gdb) p tmp_br_zif
$1 = (struct zebra_if *) 0x0
(gdb) p vlan_zif->link
$2 = (struct interface *) 0x557f31fb2d40
(gdb) p vlan_zif->link->info
$3 = (void *) 0x0
(gdb) p zebra_if->ifp->name
No symbol "zebra_if" in current context.
(gdb) p vlan_zif->ifp->name
$4 = "peerlink-3.4094\000\000\000\000"

Ticket:CM-32435
Reviewed By:CCR-10957
Testing Done:

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