[l3vpn]Stale flow entries not getting removed even when all the VM config are deleted

Topology
=================================
3CSS, 1 DC-GW, 6 VMs, 2 each on each CSS.

Build used
==================================
distribution-karaf-0.6.0-20170519.042001-5322.zip

Steps to repro
==================================
1)Do the basic vxlan configuration for one CSS.
2)Configure mpls over gre.Check it is configured properly.
3)Form bgp neigborship between Controller and DC-GW and check check bgp neighborship.
4)Configure two VMs on CSS-1, two VM on CSS-2 using nova command,
5)configure bgvpn update with one rd.Check whether it is advertised to DC-GW.
6)Check these VM entries updated in "show ip route" in vpn context.
7)Delete router interface and all other nova VMs and related configurations.
8)Check flows in CSS-1, CSS-2, flow should be removed from table21, as these VMs dont exist only
but still there flows are seen.

Logs
======================================
Logs are attached.