MINOR: mux-h1: clean up conditions to enabled and disabled splicing

First, there is no reason to announce the splicing support at the
conn-stream level when it is created, at least for now. GTUNE_USE_SPLICE
option is already handled at the stream level.

Second, in h1_rcv_buf(), there is no reason to test the message state to
switch the H1C in splicing mode (via H1C_F_WANT_SPLICE flag).
h1_process_input() already takes care to set CS_FL_MAY_SPLICE flag on the
conn-stream when appropriate. Thus, in h1_rcv_buf(), we can rely on this
flag to change the H1C state.

Finally, if h1_rcv_pipe() is called, it means the H1C is already in the
splicing mode. H1C_F_WANT_SPLICE flag is necessarily already set. Thus no
reason to force it.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index 89817df..9e40887 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -586,11 +586,6 @@
 	if (h1s->flags & H1S_F_NOT_FIRST)
 		cs->flags |= CS_FL_NOT_FIRST;
 
-	if (global.tune.options & GTUNE_USE_SPLICE) {
-		TRACE_STATE("notify the mux can use splicing", H1_EV_STRM_NEW, h1s->h1c->conn, h1s);
-		cs->flags |= CS_FL_MAY_SPLICE;
-	}
-
 	if (stream_create_from_cs(cs, input) < 0) {
 		TRACE_DEVEL("leaving on stream creation failure", H1_EV_STRM_NEW|H1_EV_STRM_END|H1_EV_STRM_ERR, h1s->h1c->conn, h1s);
 		goto err;
@@ -616,11 +611,6 @@
 		goto err;
 	}
 
-	if (global.tune.options & GTUNE_USE_SPLICE) {
-		TRACE_STATE("notify the mux can use splicing", H1_EV_STRM_NEW, h1s->h1c->conn, h1s);
-		h1s->cs->flags |= CS_FL_MAY_SPLICE;
-	}
-
 	h1s->h1c->flags |= H1C_F_ST_READY;
 	TRACE_LEAVE(H1_EV_STRM_NEW, h1s->h1c->conn, h1s);
 	return h1s->cs;
@@ -3349,11 +3339,9 @@
 	else
 		TRACE_DEVEL("h1c ibuf not allocated", H1_EV_H1C_RECV|H1_EV_H1C_BLK, h1c->conn);
 
-	if (flags & CO_RFL_BUF_FLUSH) {
-		if (h1m->state == H1_MSG_TUNNEL || (h1m->state == H1_MSG_DATA && h1m->curr_len)) {
-			h1c->flags |= H1C_F_WANT_SPLICE;
-			TRACE_STATE("Block xprt rcv_buf to flush stream's buffer (want_splice)", H1_EV_STRM_RECV, h1c->conn, h1s);
-		}
+	if ((flags & CO_RFL_BUF_FLUSH) && (cs->flags & CS_FL_MAY_SPLICE)) {
+		h1c->flags |= H1C_F_WANT_SPLICE;
+		TRACE_STATE("Block xprt rcv_buf to flush stream's buffer (want_splice)", H1_EV_STRM_RECV, h1c->conn, h1s);
 	}
 	else {
 		if (((flags & CO_RFL_KEEP_RECV) || (h1m->state != H1_MSG_DONE)) && !(h1c->wait_event.events & SUB_RETRY_RECV))
@@ -3451,10 +3439,6 @@
 		goto end;
 	}
 
-	if (!(h1c->flags & H1C_F_WANT_SPLICE)) {
-		h1c->flags |= H1C_F_WANT_SPLICE;
-		TRACE_STATE("Block xprt rcv_buf to perform splicing", H1_EV_STRM_RECV, cs->conn, h1s);
-	}
 	if (h1s_data_pending(h1s)) {
 		TRACE_STATE("flush input buffer before splicing", H1_EV_STRM_RECV, cs->conn, h1s);
 		goto end;