MEDIUM: mux: Use the mux protocol specified on bind/server lines

To do so, mux choices are split to handle incoming and outgoing connections in a
different way. The protocol specified on the bind/server line is used in
priority. Then, for frontend connections, the ALPN is retrieved and used to
choose the best mux. For backend connection, there is no ALPN. Finaly, if no
protocol is specified and no protocol matches the ALPN, we fall back on a
default mux, choosing in priority the first mux with exactly the same mode.
diff --git a/src/backend.c b/src/backend.c
index 50ef3b7..1aadca5 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -1189,7 +1189,7 @@
 		else
 			return SF_ERR_INTERNAL;  /* how did we get there ? */
 
-		conn_install_best_mux(srv_conn, s->be->mode == PR_MODE_HTTP, srv_cs);
+		conn_install_mux_be(srv_conn, srv_cs);
 
 		/* process the case where the server requires the PROXY protocol to be sent */
 		srv_conn->send_proxy_ofs = 0;