SFCOFL2 PacketIn handler throws NPE if no flow cookie is available

This has to be fixed both in master and stable/lithium.

2015-06-16 03:43:49,221 | ERROR | pool-43-thread-1 | FatalExceptionHandler | 186 - com.lmax.disruptor - 3.3.0 | Exception processing: 7 org.opendaylight.controller.md.sal.dom.broker.impl.DOMNotificationRouterEvent@14bc61a

java.lang.NullPointerException
at org.opendaylight.sfc.l2renderer.openflow.SfcL2FlowProgrammerOFimpl.compareClassificationTableCookie(SfcL2FlowProgrammerOFimpl.java:143)
at org.opendaylight.sfc.l2renderer.openflow.SfcIpv4PacketInHandler.onPacketReceived(SfcIpv4PacketInHandler.java:66)
at org.opendaylight.yangtools.yang.binding.util.NotificationListenerInvoker.invokeNotification(NotificationListenerInvoker.java:91 [69:org.opendaylight.yangtools.yang-binding:0.7.0.SNAPSHOT]
at org.opendaylight.controller.md.sal.binding.impl.BindingDOMNotificationListenerAdapter.onNotification(BindingDOMNotificationListenerAdapter.java:44)[192:org.opendaylight.controller.sal-binding-broker-impl:1.2.0.SNAPSHOT]
at org.opendaylight.controller.md.sal.dom.broker.impl.DOMNotificationRouterEvent.deliverNotification(DOMNotificationRouterEvent.java:50)[189:org.opendaylight.controller.sal-broker-impl:1.2.0.SNAPSHOT]
at org.opendaylight.controller.md.sal.dom.broker.impl.DOMNotificationRouter$1.onEvent(DOMNotificationRouter.java:68)[189:org.opendaylight.controller.sal-broker-impl:1.2.0.SNAPSHOT]
at org.opendaylight.controller.md.sal.dom.broker.impl.DOMNotificationRouter$1.onEvent(DOMNotificationRouter.java:65)[189:org.opendaylight.controller.sal-broker-impl:1.2.0.SNAPSHOT]
at com.lmax.disruptor.BatchEventProcessor.run(BatchEventProcessor.java:128)[186:com.lmax.disruptor:3.3.0]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)[:1.7.0_75]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)[:1.7.0_75]
at java.lang.Thread.run(Thread.java:745)[:1.7.0_75]