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/libmsc/vty_interface_layer3.c b/openbsc/src/libmsc/vty_interface_layer3.c
index 6ac2c65..1d0097a 100644
--- a/openbsc/src/libmsc/vty_interface_layer3.c
+++ b/openbsc/src/libmsc/vty_interface_layer3.c
@@ -764,7 +764,7 @@
 
 int bsc_vty_init_extra(void)
 {
-	register_signal_handler(SS_SCALL, scall_cbfn, NULL);
+	osmo_signal_register_handler(SS_SCALL, scall_cbfn, NULL);
 
 	install_element_ve(&show_subscr_cmd);
 	install_element_ve(&show_subscr_cache_cmd);