vxlan ports should not be removed in table 110 flow entry unless last VM instance removed from the openstack node.

ODL version: stable/beryllium (netvirt)

Issue Scenario :
while deleting VM instance from the openstack node Vxlan ports are removed from the table 110 flood entry.
created 2 VM instance in compute node using network and deleted 1 VM, still 1 VM presented in compute node but the vxlan ports is removed
so the Broadcast packets generated from the VM in compute node are dropped, broadcast packets not reaching neighbor nodes.

Reproduce the Bug :
I have control node and 2 compute nodes connected to ODL controller.
created network and 6 VM instance.
2VM instance in control node.
2VM instance in compute node1.
2VM instance in compute node2.
Now deleted 1VM instance from compute node2, vxlan port of compute node1 and control node is removed in compute node2 flood entry.

dump flows after creating VM instance in compute node2:

cookie=0x0, duration=1484.310s, table=100, n_packets=17, n_bytes=2626, priority=0 actions=goto_table:110

cookie=0x0, duration=18.572s, table=110, n_packets=0, n_bytes=0, tun_id=0x41d,dl_dst=fa:16:3e:98:48:6b actions=output:3

cookie=0x0, duration=17.140s, table=110, n_packets=0, n_bytes=0, tun_id=0x41d,dl_dst=fa:16:3e:f1:b9:f6 actions=output:5

cookie=0x0, duration=18.563s, table=110, n_packets=0, n_bytes=0, priority=16384,reg0=0x2,tun_id=0x41d,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 actions=output:3,output:5

cookie=0x0, duration=18.557s, table=110, n_packets=0, n_bytes=0, priority=16383,reg0=0x1,tun_id=0x41d,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 actions=output:3,output:1,output:2,output:5 -->(port 1 and 2 belongs to Vxlan, port 3 and 5 belongs to VM)

cookie=0x0, duration=18.548s, table=110, n_packets=0, n_bytes=0, priority=8192,tun_id=0x41d actions=drop

cookie=0x0, duration=1484.310s, table=110, n_packets=17, n_bytes=2626, priority=0 actions=drop

port details:

[stack@compute2 devstack]$ sudo ovs-vsctl list interface | grep -e "ofport|vxlan"

name : "vxlan-10.106.138.139"
ofport : 1
ofport_request : []
type : vxlan
name : "vxlan-10.106.138.141"
ofport : 2
ofport_request : []
type : vxlan

dump flows after deleting 1 VM instance in compute node2:

cookie=0x0, duration=1857.101s, table=100, n_packets=92, n_bytes=16262, priority=0 actions=goto_table:110

cookie=0x0, duration=391.363s, table=110, n_packets=2, n_bytes=711, tun_id=0x41d,dl_dst=fa:16:3e:98:48:6b actions=output:3

cookie=0x0, duration=391.354s, table=110, n_packets=0, n_bytes=0, priority=16384,reg0=0x2,tun_id=0x41d,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 actions=output:3

cookie=0x0, duration=391.348s, table=110, n_packets=16, n_bytes=2284, priority=16383,reg0=0x1,tun_id=0x41d,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 actions=output:3(removed VM present in the port 5, vxlan ports also removed)

cookie=0x0, duration=1857.101s, table=110, n_packets=54, n_bytes=10896, priority=0 actions=drop