Modules compatibility: peer.notify.

This callback can be used to notify balancer about various events.
For now, it is only used in nginx-plus.
diff --git a/src/event/ngx_event_connect.h b/src/event/ngx_event_connect.h
index 25809d0..f410d35 100644
--- a/src/event/ngx_event_connect.h
+++ b/src/event/ngx_event_connect.h
@@ -25,6 +25,8 @@
     void *data);
 typedef void (*ngx_event_free_peer_pt)(ngx_peer_connection_t *pc, void *data,
     ngx_uint_t state);
+typedef void (*ngx_event_notify_peer_pt)(ngx_peer_connection_t *pc,
+    void *data, ngx_uint_t type);
 #if (NGX_SSL)
 
 typedef ngx_int_t (*ngx_event_set_peer_session_pt)(ngx_peer_connection_t *pc,
@@ -46,6 +48,7 @@
 
     ngx_event_get_peer_pt            get;
     ngx_event_free_peer_pt           free;
+    ngx_event_notify_peer_pt         notify;
     void                            *data;
 
 #if (NGX_SSL)