Flow is not deleted in Controller Node after Virtual NW deleted.

Environment Details:
OpenStack Version: stable/ocata
ODL Version: carbon-FR + L2GW related patches

Issue:
Flow is not deleted in Controller Node after Virtual NW deleted.
The flow is "table=36, priority=5, tun_id=0x.. " like below:
cookie=0x9001389, table=36, priority=5,tun_id=0x42a actions=write_metadata:0x1389000000/0xfffffffff000000,goto_table:51

Also checked http://127.0.0.1:8181/restconf/config/opendaylight-inventory:nodes/ and found that the flow with 'flow-name' as 'ITM Flow Entry :xxxx' is not deleted.

Reproduction steps:
1. Create NW
neutron net-create test-nw
neutron subnet-create test-nw 192.168.0.0/24 --enable-dhcp
2. Delete NW
neutron net-delete test-nw