Rename stats for HTTP/2 current client connections
Rename stats for HTTP/2 current client connections

It is called `proxy.process.http2.current_client_sessions` but it should be
`proxy.process.http2.current_client_connections` for consistency.

duke8253/trafficserver,vmamidi/trafficserver,vmamidi/trafficserver,dyrock/trafficserver,bryancall/trafficserver,pbchou/trafficserver,davidbz/trafficserver,duke8253/trafficserver,dyrock/trafficserver,pbchou/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,dyrock/trafficserver,davidbz/trafficserver,davidbz/trafficserver,davidbz/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,chitianhao/trafficserver,dyrock/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,duke8253/trafficserver,duke8253/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,bryancall/trafficserver,dyrock/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,davidbz/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,chitianhao/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,chitianhao/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,dyrock/trafficserver,dyrock/trafficserver,chitianhao/trafficserver