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/handover_logic.c b/openbsc/src/libbsc/handover_logic.c
index bf9588b..1aa8fde 100644
--- a/openbsc/src/libbsc/handover_logic.c
+++ b/openbsc/src/libbsc/handover_logic.c
@@ -344,7 +344,7 @@
 
 	sig_ho.old_lchan = ho->old_lchan;
 	sig_ho.new_lchan = new_lchan;
-	dispatch_signal(SS_HO, S_HANDOVER_ACK, &sig_ho);
+	osmo_signal_dispatch(SS_HO, S_HANDOVER_ACK, &sig_ho);
 	return 0;
 }
 
@@ -388,6 +388,6 @@
 
 static __attribute__((constructor)) void on_dso_load_ho_logic(void)
 {
-	register_signal_handler(SS_LCHAN, ho_logic_sig_cb, NULL);
-	register_signal_handler(SS_ABISIP, ho_logic_sig_cb, NULL);
+	osmo_signal_register_handler(SS_LCHAN, ho_logic_sig_cb, NULL);
+	osmo_signal_register_handler(SS_ABISIP, ho_logic_sig_cb, NULL);
 }