MNCC: rename mncc_send() to mncc_tx_to_cc()

This name clearly indicates: MNCC api transmits to Call Control,
i.e. down from the L4/application into the L3 04.08 code.
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index b91ce6a..634eed3 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -2818,7 +2818,7 @@
 	(sizeof(downstatelist) / sizeof(struct downstate))
 
 
-int mncc_send(struct gsm_network *net, int msg_type, void *arg)
+int mncc_tx_to_cc(struct gsm_network *net, int msg_type, void *arg)
 {
 	int i, rc = 0;
 	struct gsm_trans *trans = NULL, *transt;