FRS uses SwitchFlowId and not FlowDescriptor

Forwardingrules-synchronizer (FRS) currently uses as unique flow identifier SwitchFlowId (combination of table-id, priority and match) and not FlowDescriptor(combination of table-id and flow-id). Therefore it performs removeFlow and addFlow actions instead of updateFlow if we updated flow in datastore. As it is datastore dependent application it should probably follows datastore type of modification and not the switch view (or both?).