Only call update metrics if packet in handler returned some flows.
Only call update metrics if packet in handler returned some flows.

byllyfish/faucet,shivarammysore/faucet,mwutzke/faucet,faucetsdn/faucet,faucetsdn/faucet,gizmoguy/faucet,mwutzke/faucet,trungdtbk/faucet,shivarammysore/faucet,trungdtbk/faucet,REANNZ/faucet,gizmoguy/faucet,wackerly/faucet,anarkiwi/faucet,REANNZ/faucet,anarkiwi/faucet,trentindav/faucet,trentindav/faucet,byllyfish/faucet,wackerly/faucet