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/silent_call.c b/openbsc/src/libmsc/silent_call.c
index 9e9b72d..6a188c8 100644
--- a/openbsc/src/libmsc/silent_call.c
+++ b/openbsc/src/libmsc/silent_call.c
@@ -56,13 +56,13 @@
 			conn->lchan->ts->nr, conn->lchan->ts->trx->arfcn);
 		conn->silent_call = 1;
 		/* increment lchan reference count */
-		dispatch_signal(SS_SCALL, S_SCALL_SUCCESS, &sigdata);
+		osmo_signal_dispatch(SS_SCALL, S_SCALL_SUCCESS, &sigdata);
 		break;
 	case GSM_PAGING_EXPIRED:
 	case GSM_PAGING_BUSY:
 	case GSM_PAGING_OOM:
 		DEBUGP(DSMS, "expired\n");
-		dispatch_signal(SS_SCALL, S_SCALL_EXPIRED, &sigdata);
+		osmo_signal_dispatch(SS_SCALL, S_SCALL_EXPIRED, &sigdata);
 		break;
 	default:
 		rc = -EINVAL;