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/bts_ericsson_rbs2000.c b/openbsc/src/libbsc/bts_ericsson_rbs2000.c
index 95bf38b..c2ae0e7 100644
--- a/openbsc/src/libbsc/bts_ericsson_rbs2000.c
+++ b/openbsc/src/libbsc/bts_ericsson_rbs2000.c
@@ -257,9 +257,9 @@
 	gsm_btsmodel_set_feature(&model_rbs2k, BTS_FEAT_HOPPING);
 	gsm_btsmodel_set_feature(&model_rbs2k, BTS_FEAT_HSCSD);
 
-	register_signal_handler(SS_INPUT, inp_sig_cb, NULL);
-	register_signal_handler(SS_GLOBAL, gbl_sig_cb, NULL);
-	register_signal_handler(SS_NM, nm_sig_cb, NULL);
+	osmo_signal_register_handler(SS_INPUT, inp_sig_cb, NULL);
+	osmo_signal_register_handler(SS_GLOBAL, gbl_sig_cb, NULL);
+	osmo_signal_register_handler(SS_NM, nm_sig_cb, NULL);
 
 	return gsm_bts_model_register(&model_rbs2k);
 }