tm: default value for failure_reply_mode set to 3

- discard previous replies if a new serial forking step is done

(cherry picked from commit 8118c85bc53494c5a1d6e0a9fd655778f8ca8b61)

modules/tm/t_reply.c

@@ -191,7 +191,7 @@ extern int tm_remap_503_500;
  * - 3 - all branches are discarded if a new leg of serial forking
  *       is started (default kamailio 1.5.x behaviour)
  */
-int failure_reply_mode = 0;
+int failure_reply_mode = 3;
 
 /* responses priority (used by t_pick_branch)
  *  0xx is used only for the initial value (=> should have no chance to be