MINOR: muxes: Rely on conn_is_back() during init to handle front/back conn

Instead of using the connection context to make the difference between a
frontend connection and a backend connection, we now rely on the function
conn_is_back().
diff --git a/src/mux_h1.c b/src/mux_h1.c
index 4dcbcaf..a40ef3f 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -287,33 +287,34 @@
 	if (!conn_is_back(h1c->conn)) {
 		if (h1c->px->options2 & PR_O2_REQBUG_OK)
 			h1s->req.err_pos = -1;
+
+		/* For frontend connections we should always have a session */
+		if (!sess)
+			sess = h1c->conn->owner;
+
+		h1s->csinfo.create_date = sess->accept_date;
+		h1s->csinfo.tv_create   = sess->tv_accept;
+		h1s->csinfo.t_handshake = sess->t_handshake;
+		h1s->csinfo.t_idle      = -1;
 	}
 	else {
 		if (h1c->px->options2 & PR_O2_RSPBUG_OK)
 			h1s->res.err_pos = -1;
-	}
 
-	/* If a conn_stream already exists, attach it to this H1S. Otherwise we
-	 * create a new one.
-	 */
-	if (cs) {
 		h1s->csinfo.create_date = date;
 		h1s->csinfo.tv_create   = now;
 		h1s->csinfo.t_handshake = 0;
 		h1s->csinfo.t_idle      = -1;
+	}
 
+	/* If a conn_stream already exists, attach it to this H1S. Otherwise we
+	 * create a new one.
+	 */
+	if (cs) {
 		cs->ctx = h1s;
 		h1s->cs = cs;
 	}
 	else {
-		/* For frontend connections we should always have a session */
-		sess = h1c->conn->owner;
-
-		h1s->csinfo.create_date = sess->accept_date;
-		h1s->csinfo.tv_create   = sess->tv_accept;
-		h1s->csinfo.t_handshake = sess->t_handshake;
-		h1s->csinfo.t_idle      = -1;
-
 		cs = h1s_new_cs(h1s);
 		if (!cs)
 			goto fail;
@@ -384,7 +385,7 @@
 	h1c->wait_event.task->context = h1c;
 	h1c->wait_event.events   = 0;
 
-	if (conn->ctx) {
+	if (conn_is_back(conn)) {
 		h1c->shut_timeout = h1c->timeout = proxy->timeout.server;
 		if (tick_isset(proxy->timeout.serverfin))
 			h1c->shut_timeout = proxy->timeout.serverfin;
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 3e50150..5448ea8 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -484,7 +484,7 @@
 	if (!h2c)
 		goto fail_no_h2c;
 
-	if (conn->ctx) {
+	if (conn_is_back(conn)) {
 		h2c->flags = H2_CF_IS_BACK;
 		h2c->shut_timeout = h2c->timeout = prx->timeout.server;
 		if (tick_isset(prx->timeout.serverfin))