all VpnPortIpToPort instances are lost from ODL cache after reboot, because they are in operational DS -- this is especially critical for router interfaces that do not get ARP responses

Setup
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DEVSTACK_BRANCH: stable/Mitaka
Node version:V2
ODL_USE_DOWNSTREAM_ARTIFACTS

Description
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1.Lunch vm (ip=10.0.123.3),Associate floating ip(see ip 10.64.121.3),send ping to 8.8.8.8(external network) and try to open ssh connection from Lab to Vm - succeed
2.Restart Odl by the follow commands(via controller):
/opt/stack/opendaylight/distribution-karaf-0.5.2-SNAPSHOT/bin/stop
pkill -f opendaylight
/opt/stack/opendaylight/distribution-karaf-0.5.2-SNAPSHOT/bin/start
3.send ping to 8.8.8.8 and try to open ssh connection from Lab to Vm - fail.

Defect Description
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After ODL restart VM cannot learn private network router interface MAC address (incomplete).
Missing entry for router interface in: neutronvpn:neutron-vpn-portip-port-data after restart.