code: void returnClientChannel(HttpRoute httpRoute, Http2ClientChannel http2ClientChannel) {
          EventLoopPool.PerRouteConnectionPool perRouteConnectionPool = fetchPerRoutePool(httpRoute,
                                                                                          http2ClientChannel.getChannel()
                                                                                              .eventLoop());
          if (perRouteConnectionPool != null) {
              perRouteConnectionPool.addChannel(http2ClientChannel);
          }
      }
docs: Return the http/2 client channel to per route pool.
  
  @param httpRoute          the http route
  @param http2ClientChannel represents the http/2 client channel