OPTIM: mux-h1: subscribe rather than waking up at a few other places

This is another round of conversion from a blind tasklet_wakeup() to
a more careful subscribe(). It has significantly improved the number
of function calls per HTTP request (/?s=1k/t=20) :
                        before    after
 tasklet_wakeup:          3         2
 conn_subscribe:          3         2
 h1_iocb:                 3         2
 h1_process:              3         2
 h1_parse_msg_hdrs:       4         3
 h1_rcv_buf:              5         3
 h1_send:                 5         4
 h1_subscribe:            2         1
 h1_wake_stream_for_send: 5         4
 http_wait_for_request:   2         1
 process_stream:          3         2
 si_cs_io_cb:             4         2
 si_cs_process:           3         1
 si_cs_rcv:               5         3
 si_sync_send:            2         1
 si_update_both:          2         1
 stream_int_chk_rcv_conn: 3         2
 stream_int_notify:       3         1
 stream_release_buffers:  9         4
diff --git a/src/mux_h1.c b/src/mux_h1.c
index e7247aa..a07654b 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -695,7 +695,7 @@
 		task_queue(t);
 
 	/* Try to read, if nothing is available yet we'll just subscribe */
-	tasklet_wakeup(h1c->wait_event.tasklet);
+	h1c->conn->xprt->subscribe(h1c->conn, h1c->conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 
 	/* mux->wake will be called soon to complete the operation */
 	TRACE_LEAVE(H1_EV_H1C_NEW, conn, h1c->h1s);
@@ -1476,7 +1476,7 @@
 	if ((h1c->flags & H1C_F_IN_FULL) && buf_room_for_htx_data(&h1c->ibuf)) {
 		h1c->flags &= ~H1C_F_IN_FULL;
 		TRACE_STATE("h1c ibuf not full anymore", H1_EV_RX_DATA|H1_EV_H1C_BLK|H1_EV_H1C_WAKE);
-		tasklet_wakeup(h1c->wait_event.tasklet);
+		h1c->conn->xprt->subscribe(h1c->conn, h1c->conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 	}
 
 	h1s->cs->flags &= ~(CS_FL_RCV_MORE | CS_FL_WANT_ROOM);
@@ -1891,7 +1891,7 @@
 				}
 				else if (h1s->h1c->flags & H1C_F_IN_BUSY) {
 					h1s->h1c->flags &= ~H1C_F_IN_BUSY;
-					tasklet_wakeup(h1s->h1c->wait_event.tasklet);
+					h1c->conn->xprt->subscribe(h1c->conn, h1c->conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 					TRACE_STATE("h1c no more busy", H1_EV_TX_DATA|H1_EV_H1C_BLK|H1_EV_H1C_WAKE, h1c->conn, h1s);
 				}
 
@@ -2641,7 +2641,7 @@
 			TRACE_STATE("disable splicing", H1_EV_STRM_RECV, h1c->conn, h1s);
 		}
 		if (h1m->state != H1_MSG_DONE && !(h1c->wait_event.events & SUB_RETRY_RECV))
-			tasklet_wakeup(h1c->wait_event.tasklet);
+			h1c->conn->xprt->subscribe(h1c->conn, h1c->conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 	}
 	TRACE_LEAVE(H1_EV_STRM_RECV, h1c->conn, h1s,, (size_t[]){ret});
 	return ret;