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/gsm_04_11.c b/openbsc/src/libmsc/gsm_04_11.c
index 1db307a..326c2b8 100644
--- a/openbsc/src/libmsc/gsm_04_11.c
+++ b/openbsc/src/libmsc/gsm_04_11.c
@@ -151,7 +151,7 @@
 	sig.trans = trans;
 	sig.sms = sms;
 	sig.paging_result = paging_result;
-	dispatch_signal(SS_SMS, sig_no, &sig);
+	osmo_signal_dispatch(SS_SMS, sig_no, &sig);
 }
 
 /*