Implement IuCS (large refactoring and addition)

osmo-nitb becomes osmo-msc
add DIUCS debug log constant
add iucs.[hc]
add msc vty, remove nitb vty
add libiudummy, to avoid linking Iu deps in tests
Use new msc_tx_dtap() instead of gsm0808_submit_dtap()
libmgcp: add mgcpgw client API
bridge calls via mgcpgw

Enable MSC specific CTRL commands, bsc_base_ctrl_cmds_install() still needs to
be split up.

Change-Id: I5b5b6a9678b458affa86800afb1ec726e66eed88
diff --git a/src/libmsc/transaction.c b/src/libmsc/transaction.c
index d157f54..7289a8f 100644
--- a/src/libmsc/transaction.c
+++ b/src/libmsc/transaction.c
@@ -180,15 +180,15 @@
  * \param[in] conn Connection to check
  * \returns 1 in case there is a transaction, 0 otherwise
  */
-int trans_has_conn(const struct gsm_subscriber_connection *conn)
+struct gsm_trans *trans_has_conn(const struct gsm_subscriber_connection *conn)
 {
 	struct gsm_trans *trans;
 
 	llist_for_each_entry(trans, &conn->network->trans_list, entry)
 		if (trans->conn == conn)
-			return 1;
+			return trans;
 
-	return 0;
+	return NULL;
 }
 
 /*! Free all transactions associated with a connection, presumably when the