[BUG] config: look for ID conflicts in all sockets, not only last ones.

ID conflicts between 'bind' lines were not detected due to this typo.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 5eab73d..b35a15e 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -1180,7 +1180,7 @@
 					goto out;
 				}
 
-				for (l = curproxy->listen; l != last_listen; l = l->next)
+				for (l = curproxy->listen; l; l = l->next)
 					if (curproxy->listen != l && l->luid == curproxy->listen->luid) {
 						Alert("parsing [%s:%d]: custom id has to be unique but is duplicated in %s.\n",
 							file, linenum, args[1]);