Introduced by #9094, in Http2ConnectionHanlder, when there is no active stream, doing GO_AWAY with error code NO_ERROR will immediately shut down the channel once the GO_AWAY frame is sent. This breaks higher layer implementation's logic of graceful shutdown, such as in gRPC. Now that the GOAWAY(<max id>), PING, PING(ACK), GOAWAY(<real id>) approach is left for higher layer implementations, graceful shutdown should not be initiated in Http2ConnectionHandler#goAway(...).

/cc @Scottmitch @ejona86 @carl-mastrangelo @dapengzhang0