MNCC: rename mncc_upq_enqueue() to cc_tx_to_mncc()

The new function name clearly indicates: The Call Control
(TS 04.08, msc-side in OpenBSC) wants to transmit something to the
MNCC interface.
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index 637f84f..b91ce6a 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -1341,7 +1341,7 @@
 	if (!msg)
 		return -ENOMEM;
 	memcpy(msg->data, mncc, sizeof(struct gsm_mncc));
-	mncc_upq_enqueue(net, msg);
+	cc_tx_to_mncc(net, msg);
 
 	return 0;
 }