[MINOR] frontend: only check for monitor-net rules if LI_O_CHK_MONNET is set

We can disable the monitor-net rules on a listener if this flag is not
set in the listener's options. This will be useful when we don't want
to check that fe->addr is set or not for non-TCP frontends.
diff --git a/src/frontend.c b/src/frontend.c
index 5af5582..04c3d9b 100644
--- a/src/frontend.c
+++ b/src/frontend.c
@@ -79,7 +79,7 @@
 	/* if this session comes from a known monitoring system, we want to ignore
 	 * it as soon as possible, which means closing it immediately for TCP.
 	 */
-	if (unlikely(p->mon_mask.s_addr &&
+	if (unlikely((l->options & LI_O_CHK_MONNET) &&
 		     addr->ss_family == AF_INET &&
 		     (((struct sockaddr_in *)addr)->sin_addr.s_addr & p->mon_mask.s_addr) == p->mon_net.s_addr)) {
 		if (p->mode == PR_MODE_TCP) {