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/libabis/e1_input.c b/openbsc/src/libabis/e1_input.c
index d3a5cda..dd33852 100644
--- a/openbsc/src/libabis/e1_input.c
+++ b/openbsc/src/libabis/e1_input.c
@@ -576,7 +576,7 @@
 	isd.sapi = sapi;
 
 	/* report further upwards */
-	dispatch_signal(SS_INPUT, evt, &isd);
+	osmo_signal_dispatch(SS_INPUT, evt, &isd);
 	return 0;
 }
 
@@ -612,7 +612,7 @@
 	 * configured */
 	memset(&isd, 0, sizeof(isd));
 	isd.line = line;
-	dispatch_signal(SS_INPUT, S_INP_LINE_INIT, &isd);
+	osmo_signal_dispatch(SS_INPUT, S_INP_LINE_INIT, &isd);
 
 	return rc;
 }
@@ -639,7 +639,7 @@
 {
 	tall_sigl_ctx = talloc_named_const(tall_bsc_ctx, 1,
 					   "e1inp_sign_link");
-	register_signal_handler(SS_GLOBAL, e1i_sig_cb, NULL);
+	osmo_signal_register_handler(SS_GLOBAL, e1i_sig_cb, NULL);
 
 	e1inp_misdn_init();
 #ifdef HAVE_DAHDI_USER_H