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_sccp.c b/openbsc/src/osmo-bsc/osmo_bsc_sccp.c
index 099552b..f4cdf36 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_sccp.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_sccp.c
@@ -282,7 +282,7 @@
 	sccp_connection_set_incoming(&sccp_ssn_bssap, msc_sccp_accept, NULL);
 	sccp_set_read(&sccp_ssn_bssap, msc_sccp_read, gsmnet);
 
-	register_signal_handler(SS_MSC, handle_msc_signal, gsmnet);
+	osmo_signal_register_handler(SS_MSC, handle_msc_signal, gsmnet);
 
 	return 0;
 }