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/ipaccess/ipaccess-config.c b/openbsc/src/ipaccess/ipaccess-config.c
index 5cd901c..e84892c 100644
--- a/openbsc/src/ipaccess/ipaccess-config.c
+++ b/openbsc/src/ipaccess/ipaccess-config.c
@@ -908,8 +908,8 @@
 	gsm_bts_trx_alloc(bts);
 	bts->oml_tei = stream_id;
 	
-	register_signal_handler(SS_NM, nm_sig_cb, NULL);
-	register_signal_handler(SS_IPAC_NWL, nwl_sig_cb, NULL);
+	osmo_signal_register_handler(SS_NM, nm_sig_cb, NULL);
+	osmo_signal_register_handler(SS_IPAC_NWL, nwl_sig_cb, NULL);
 
 	ipac_nwl_init();