exception from Ipv6. Looks like getGatewayIP() is returning null.

https://logs.opendaylight.org/sandbox/jenkins091/netvirt-vpnservice-csit-1node-openstack-mitaka-openstack-jamo-boron/17/archives/odl1_karaf.log.gz

2016-08-23 21:24:11,883 | ERROR | n-dispatcher-389 | DataChangeListener | 174 - org.opendaylight.controller.sal-distributed-datastore - 1.4.0.SNAPSHOT | Error notifying listener org.opendaylight.netvirt.ipv6service.NeutronSubnetChangeListener
java.lang.NullPointerException
at org.opendaylight.netvirt.ipv6service.IfMgr.addSubnet(IfMgr.java:198)[320:org.opendaylight.netvirt.ipv6service-impl:0.3.0.SNAPSHOT]
at org.opendaylight.netvirt.ipv6service.NeutronSubnetChangeListener.add(NeutronSubnetChangeListener.java:81)[320:org.opendaylight.netvirt.ipv6service-impl:0.3.0.SNAPSHOT]
at org.opendaylight.netvirt.ipv6service.NeutronSubnetChangeListener.add(NeutronSubnetChangeListener.java:33)[320:org.opendaylight.netvirt.ipv6service-impl:0.3.0.SNAPSHOT]
at org.opendaylight.genius.mdsalutil.AbstractDataChangeListener.createData(AbstractDataChangeListener.java:68)[274:org.opendaylight.genius.mdsalutil-api:0.1.0.SNAPSHOT]
at org.opendaylight.genius.mdsalutil.AbstractDataChangeListener.onDataChanged(AbstractDataChangeListener.java:54)[274:org.opendaylight.genius.mdsalutil-api:0.1.0.SNAPSHOT]
at org.opendaylight.controller.md.sal.binding.impl.AbstractForwardedDataBroker$TranslatingDataChangeInvoker.onDataChanged(AbstractForwardedDataBroker.java:143)[145:org.opendaylight.controller.sal-binding-broker-impl:1.4.0.SNAPSHOT]
at org.opendaylight.controller.cluster.datastore.DataChangeListener.dataChanged(DataChangeListener.java:71)[174:org.opendaylight.controller.sal-distributed-datastore:1.4.0.SNAPSHOT]
at org.opendaylight.controller.cluster.datastore.DataChangeListener.handleReceive(DataChangeListener.java:43)[174:org.opendaylight.controller.sal-distributed-datastore:1.4.0.SNAPSHOT]
at org.opendaylight.controller.cluster.common.actor.AbstractUntypedActor.onReceive(AbstractUntypedActor.java:26)[169:org.opendaylight.controller.sal-clustering-commons:1.4.0.SNAPSHOT]
at akka.actor.UntypedActor$$anonfun$receive$1.applyOrElse(UntypedActor.scala:165)[157:com.typesafe.akka.actor:2.4.7]
at akka.actor.Actor$class.aroundReceive(Actor.scala:484)[157:com.typesafe.akka.actor:2.4.7]
at akka.actor.UntypedActor.aroundReceive(UntypedActor.scala:95)[157:com.typesafe.akka.actor:2.4.7]
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:526)[157:com.typesafe.akka.actor:2.4.7]
at akka.actor.ActorCell.invoke(ActorCell.scala:495)[157:com.typesafe.akka.actor:2.4.7]
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)[157:com.typesafe.akka.actor:2.4.7]
at akka.dispatch.Mailbox.run(Mailbox.scala:224)[157:com.typesafe.akka.actor:2.4.7]
at akka.dispatch.Mailbox.exec(Mailbox.scala:234)[157:com.typesafe.akka.actor:2.4.7]
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)[153:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)[153:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]
at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)[153:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]
at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)[153:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]