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/chan_alloc.c b/openbsc/src/libbsc/chan_alloc.c
index ff745f5..cfd3874 100644
--- a/openbsc/src/libbsc/chan_alloc.c
+++ b/openbsc/src/libbsc/chan_alloc.c
@@ -284,7 +284,7 @@
 		struct challoc_signal_data sig;
 		sig.bts = bts;
 		sig.type = type;
-		dispatch_signal(SS_CHALLOC, S_CHALLOC_ALLOC_FAIL, &sig);
+		osmo_signal_dispatch(SS_CHALLOC, S_CHALLOC_ALLOC_FAIL, &sig);
 	}
 
 	return lchan;
@@ -306,7 +306,7 @@
 		/* We might kill an active channel... */
 		sig.lchan = lchan;
 		sig.mr = NULL;
-		dispatch_signal(SS_LCHAN, S_LCHAN_UNEXPECTED_RELEASE, &sig);
+		osmo_signal_dispatch(SS_LCHAN, S_LCHAN_UNEXPECTED_RELEASE, &sig);
 	}
 
 
@@ -330,7 +330,7 @@
 
 	sig.lchan = lchan;
 	sig.bts = lchan->ts->trx->bts;
-	dispatch_signal(SS_CHALLOC, S_CHALLOC_FREED, &sig);
+	osmo_signal_dispatch(SS_CHALLOC, S_CHALLOC_FREED, &sig);
 
 	if (lchan->conn) {
 		LOGP(DRLL, LOGL_ERROR, "the subscriber connection should be gone.\n");