zebra: Refactoring changes for zebra_evpn_map_vlan zebra_evpn_from_svi and zl3vni_fro...

zebra: Refactoring changes for zebra_evpn_map_vlan zebra_evpn_from_svi and zl3vni_from_svi

Today to find the vni for a given (vlan, bridge) we walk over all interfaces
and filter the vxlan device associated with the bridge. With multiple vlan aware
bridge changes, we can derive the vni directly by looking up the hash table i.e.
the vlan_table of the associated (vlan, bridge) which would give the vni.

During vrf_terminate() call zebra_l2_bridge_if_cleanup if the interface
that we are removing is of type bridge. In this case, we walk over all
the vlan<->access_bd association and clean them up.

zebra_evpn_t is modified to record (vlan, bridge) details and the
corresponding vty is modified to print the same.
zevpn_bridge_if_set and zl3vni_bridge_if_set is used to set/unset the
association.

Signed-off-by: Sharath Ramamurthy <sramamurthy@nvidia.com>