Stale flows in table 0,20, 21,19  and group entries after neutron port-delete of all ports

Test Steps:

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Initial configuration:

->Configure 8 dualstack networks and 16 VMs and 2 routers. Two computes have one VM for each of the 8 networks. Attach 4 dualstack networks to each router

->Configure BGP, 2 VPN instances .

->Attach routers to VPN instances.

->Configure extra routes with four VMs as nexthops for both the routers.

->Verify reachability between DCGW and extraroute.

Delete configuration:

->Dissociate routers from VPN

-> router update no routes on both routes

-> delete all subnets from the router

->delete all VPN instances

->Delete all routers

 ->Delete all VMs

->Delete all neutron ports

Stale flows are seen in table 0, 20 21 and 19 and group entries. Stale flows file is attached