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/token_auth.c b/openbsc/src/libmsc/token_auth.c
index b9e481d..cf26ba8 100644
--- a/openbsc/src/libmsc/token_auth.c
+++ b/openbsc/src/libmsc/token_auth.c
@@ -148,6 +148,6 @@
 //static __attribute__((constructor)) void on_dso_load_token(void)
 void on_dso_load_token(void)
 {
-	register_signal_handler(SS_SUBSCR, token_subscr_cb, NULL);
-	register_signal_handler(SS_SMS, token_sms_cb, NULL);
+	osmo_signal_register_handler(SS_SUBSCR, token_subscr_cb, NULL);
+	osmo_signal_register_handler(SS_SMS, token_sms_cb, NULL);
 }