Added in NXMs for source and destination tunnel IPs, included in new Loxigen 0.9.0. Used Loxigen's OFFlowModFlags serializers for different OFVersions to fix compile error in StatsReplySerializer introduced upon Loxigen upgrade. Add new OF1.4 counters to DebugCounters to allow unit tests to compile (this is the first step in OF1.4 support =) ).