MNCC: pass the actual 'struct msgb' down the mncc_recv() callback

this is required as we no longer have a dequeue-handler that can take
care of free()ing the message after passing it to the MNCC handler.
diff --git a/openbsc/src/mncc.c b/openbsc/src/mncc.c
index d20b4ef..34093a8 100644
--- a/openbsc/src/mncc.c
+++ b/openbsc/src/mncc.c
@@ -110,7 +110,5 @@
 
 void cc_tx_to_mncc(struct gsm_network *net, struct msgb *msg)
 {
-	struct gsm_mncc *mncc = msgb_data(msg);
-
-	net->mncc_recv(net, mncc->msg_type, mncc);
+	net->mncc_recv(net, msg);
 }