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/osmo-bsc/osmo_bsc_rf.c b/openbsc/src/osmo-bsc/osmo_bsc_rf.c
index 5ce6bf5..78550d7 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_rf.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_rf.c
@@ -137,7 +137,7 @@
 	sig.net = rf->gsm_network;
 
 	rf->policy = val;
-	dispatch_signal(SS_RF, val, &sig);
+	osmo_signal_dispatch(SS_RF, val, &sig);
 }
 
 static int switch_rf_off(struct osmo_bsc_rf *rf)