MINOR: stream-int: use si_release_endpoint() to close idle conns

We don't want to open-code the connection close code in
si_idle_conn_wake_cb() because we need to centralize some controls.

src/stream_interface.c

@@ -515,10 +515,7 @@ static int si_idle_conn_wake_cb(struct connection *conn)
 
 	if (conn->flags & (CO_FL_ERROR | CO_FL_SOCK_RD_SH)) {
 		/* warning, we can't do anything on <conn> after this call ! */
-		LIST_DEL(&conn->list);
-		conn_force_close(conn);
-		conn_free(conn);
-		si->end = NULL;
+		si_release_endpoint(si);
 		return -1;
 	}
 	return 0;