[MEDIUM] listeners: queue proxy-bound listeners at the proxy's

All listeners that are limited by a proxy-specific resource are now
queued at the proxy's and not globally. This allows finer-grained
wakeups when releasing resource.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index fea8a5e..9bda578 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -301,6 +301,7 @@
 	struct pxcounters be_counters;		/* backend statistics counters */
 	struct pxcounters fe_counters;		/* frontend statistics counters */
 
+	struct list listener_queue;		/* list of the temporarily limited listeners because of lack of a proxy resource */
 	struct stktable table;			/* table for storing sticking sessions */
 
 	int grace;				/* grace time after stop request */