issue a signal once a subscriber is attached or detached
diff --git a/openbsc/include/openbsc/signal.h b/openbsc/include/openbsc/signal.h
index 2ce812d..8f0f8cb 100644
--- a/openbsc/include/openbsc/signal.h
+++ b/openbsc/include/openbsc/signal.h
@@ -38,6 +38,7 @@
 	SS_ABISIP,
 	SS_NM,
 	SS_LCHAN,
+	SS_SUBSCR,
 };
 
 /* SS_PAGING signals */
@@ -69,6 +70,12 @@
 	S_LCHAN_UNEXPECTED_RELEASE,
 };
 
+/* SS_SUBSCR signals */
+enum signal_subscr {
+	S_SUBSCR_ATTACHED,
+	S_SUBSCR_DETACHED,
+};
+
 typedef int signal_cbfn(unsigned int subsys, unsigned int signal,
 			void *handler_data, void *signal_data);