zebra: fix crash in evpn neigh cleanup all

zebra: fix crash in evpn neigh cleanup all

zebra crash is seen during shutdown (frr restart).

During shutdown, remote neigh and remote mac clean up
is triggered first, followed by per vni all neigh
(including local) and macs cleanup is triggered.

The crash occurs when a remote mac is cleaned up first
and its reference is remained in local neigh.
When local neigh attempt removes itself from its associated
mac's neigh_list it triggers inaccessible memory crash.

The fix is during mac deletion if its neigh_list is non-empty
then retain the MAC in AUTO state.
This can arise when MAC and neigh duo are in different state
(remote/local). Otherwise, the order of cleanup operation
is neighs followed by macs.

The auto mac will be cleaned up when per vni all neighs and macs
are cleaned up.

Ticket:CM-29826
Reviewed By:CCR-10369
Testing Done:

Configure evpn symmetric config where
MAC is in remote state and neigh is in local state.
Perform frr restart then crash is not seen.

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