zebra: multiple vlan aware bridge data structure and related changes

zebra: multiple vlan aware bridge data structure and related changes

Multiple vlan aware bridge data structure changes and its corresponding bridge
handling changes.
A new vlan-table is maintained for each bridge which records the zebra_l2_bridge_vlan
entry. zebra_l2_bridge_vlan maps vlan to access_bd associated to this bridge.

Existing zebra_evpn_access_bd structure is vlan aware which is now modified to be
(vlan, bridge) aware.

Whenever a new access_bd is instantiated, a corresponding entry is also recorded
in the zebra l2 bridge for the vlan.
When the access_bd is dereferenced or whenever a bridge is deleted, the
association is cleaned up.

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