MINOR: listeners: export enable_listener()

we'll soon call it from outside.
diff --git a/include/haproxy/listener.h b/include/haproxy/listener.h
index e2574e6..ccd9a47 100644
--- a/include/haproxy/listener.h
+++ b/include/haproxy/listener.h
@@ -48,6 +48,14 @@
  */
 int resume_listener(struct listener *l);
 
+/* This function adds the specified listener's file descriptor to the polling
+ * lists if it is in the LI_LISTEN state. The listener enters LI_READY or
+ * LI_FULL state depending on its number of connections. In daemon mode, we
+ * also support binding only the relevant processes to their respective
+ * listeners. We don't do that in debug mode however.
+ */
+void enable_listener(struct listener *listener);
+
 /* This function adds all of the protocol's listener's file descriptors to the
  * polling lists when they are in the LI_LISTEN state. It is intended to be
  * used as a protocol's generic enable_all() primitive, for use after the
diff --git a/src/listener.c b/src/listener.c
index 30d12e9..9bc1097 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -276,7 +276,7 @@
  * also support binding only the relevant processes to their respective
  * listeners. We don't do that in debug mode however.
  */
-static void enable_listener(struct listener *listener)
+void enable_listener(struct listener *listener)
 {
 	HA_SPIN_LOCK(LISTENER_LOCK, &listener->lock);
 	if (listener->state == LI_LISTEN) {