Fix a bug that current_active_client_connections doesn't decrease
Fix a bug that current_active_client_connections doesn't decrease

The metric was not decremented when a connection is closed by graceful
shutdown (GOAWAY frame with stream ID 2^31-1).

bryancall/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,duke8253/trafficserver,duke8253/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,bryancall/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,duke8253/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,bryancall/trafficserver,pbchou/trafficserver,vmamidi/trafficserver