[VxlanMgr] changes for EVPN VXLAN (sonic-net#1266)

* VxlanMgr changes for EVPN VXLAN

1. Add support for EVPN NVO config table.
2. VxlanTunnel and TunnelMap handlers are enhanced to also cache the data so that this can be used during the deletion.
3. ARP suppression changes
4. Create state db for vxlanmgr and vlanmgr to sync the tunnel association to vlan
5. Changes to support warm reboot.

Signed-off-by: Rajesh Sankaran <[email protected]>

Author: srj102