SouthboundHandler: isUpdateOfInterest is too inclusive

isUpdateOfInterest is taking the approach of excluding updates we don't care about. This logic is incomplete as Controller, Manager, QoS, Queue, SSL, IPFIX, Flow_Table_Collector_Set etc.... will trigger southbound events.

This method should therefore be re-factored to implicitly include only the Port and Interface updates that we care about and exclude everything else.

This is far more future proof as additional tables in the Open_vSwitch schema will be excluded by default.