MEDIUM: connections: Get ride of the xprt_done callback.

The xprt_done_cb callback was used to defer some connection initialization
until we're connected and the handshake are done. As it mostly consists of
creating the mux, instead of using the callback, introduce a conn_create_mux()
function, that will just call conn_complete_session() for frontend, and
create the mux for backend.
In h2_wake(), make sure we call the wake method of the stream_interface,
as we no longer wakeup the stream task.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index d1e9316..9c1a77e 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -3650,6 +3650,7 @@
 
 	TRACE_ENTER(H2_EV_H2C_WAKE, conn);
 	ret = h2_process(h2c);
+	h2_wake_some_streams(h2c, 0);
 	TRACE_LEAVE(H2_EV_H2C_WAKE);
 	return ret;
 }