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/gprs/gb_proxy_main.c b/openbsc/src/gprs/gb_proxy_main.c
index b0fb664..9ef9098 100644
--- a/openbsc/src/gprs/gb_proxy_main.c
+++ b/openbsc/src/gprs/gb_proxy_main.c
@@ -98,7 +98,7 @@
 
 	switch (signal) {
 	case SIGINT:
-		dispatch_signal(SS_GLOBAL, S_GLOBAL_SHUTDOWN, NULL);
+		osmo_signal_dispatch(SS_GLOBAL, S_GLOBAL_SHUTDOWN, NULL);
 		sleep(1);
 		exit(0);
 		break;
@@ -239,7 +239,7 @@
 	}
 	gbcfg.nsi = bssgp_nsi;
 	gprs_ns_vty_init(bssgp_nsi);
-	register_signal_handler(SS_NS, &gbprox_signal, NULL);
+	osmo_signal_register_handler(SS_NS, &gbprox_signal, NULL);
 
 	rc = gbproxy_parse_config(config_file, &gbcfg);
 	if (rc < 0) {