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/libbsc/bsc_init.c b/openbsc/src/libbsc/bsc_init.c
index 1d14df1..0056bb0 100644
--- a/openbsc/src/libbsc/bsc_init.c
+++ b/openbsc/src/libbsc/bsc_init.c
@@ -82,7 +82,7 @@
 
 	llist_for_each_entry(bts, &net->bts_list, list) {
 		LOGP(DNM, LOGL_NOTICE, "shutting down OML for BTS %u\n", bts->nr);
-		dispatch_signal(SS_GLOBAL, S_GLOBAL_BTS_CLOSE_OM, bts);
+		osmo_signal_dispatch(SS_GLOBAL, S_GLOBAL_BTS_CLOSE_OM, bts);
 	}
 
 	return 0;
@@ -434,8 +434,8 @@
 	if (rc < 0)
 		return rc;
 
-	register_signal_handler(SS_NM, nm_sig_cb, NULL);
-	register_signal_handler(SS_INPUT, inp_sig_cb, NULL);
+	osmo_signal_register_handler(SS_NM, nm_sig_cb, NULL);
+	osmo_signal_register_handler(SS_INPUT, inp_sig_cb, NULL);
 
 	llist_for_each_entry(bts, &bsc_gsmnet->bts_list, list) {
 		rc = bootstrap_bts(bts);