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/rrlp.c b/openbsc/src/libmsc/rrlp.c
index 75bccb5..161456a 100644
--- a/openbsc/src/libmsc/rrlp.c
+++ b/openbsc/src/libmsc/rrlp.c
@@ -99,6 +99,6 @@
 
 void on_dso_load_rrlp(void)
 {
-	register_signal_handler(SS_SUBSCR, subscr_sig_cb, NULL);
-	register_signal_handler(SS_PAGING, paging_sig_cb, NULL);
+	osmo_signal_register_handler(SS_SUBSCR, subscr_sig_cb, NULL);
+	osmo_signal_register_handler(SS_PAGING, paging_sig_cb, NULL);
 }