[l3vpn_ecmp]Fib is not updated and cleared for a CSS,for extra route after all the VMs are moved out of CSS.

Steps to repro
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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 2 VMs on CSS-1 using nova command,3VMs on CSS2 configure bgvpn and route update.
Check whether it is advertised to DC-GW.
5)configure an ip on VM1 in CSS1 on int eth0:0 which was advertsised using route update.
6)Ping this ip from DC-GW.
7)Check flows
Bucket is not updating for non collocated VMs.