src: use namespace prefix osmo_signal*

Summary of changes:

s/signal_cbfn/osmo_signal_cbfn/g
s/register_signal_handler/osmo_signal_register_handler/g
s/unregister_signal_handler/osmo_signal_unregister_handler/g
s/dispatch_signal/osmo_signal_dispatch/g
diff --git a/openbsc/src/libmsc/sms_queue.c b/openbsc/src/libmsc/sms_queue.c
index 18545bf..30fa5f0 100644
--- a/openbsc/src/libmsc/sms_queue.c
+++ b/openbsc/src/libmsc/sms_queue.c
@@ -303,8 +303,8 @@
 		return -1;
 	}
 
-	register_signal_handler(SS_SUBSCR, sms_subscr_cb, network);
-	register_signal_handler(SS_SMS, sms_sms_cb, network);
+	osmo_signal_register_handler(SS_SUBSCR, sms_subscr_cb, network);
+	osmo_signal_register_handler(SS_SMS, sms_sms_cb, network);
 
 	network->sms_queue = sms;
 	INIT_LLIST_HEAD(&sms->pending_sms);