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/libvlr/vlr.c b/src/libvlr/vlr.c
index 0e0d31c..d95d1b7 100644
--- a/src/libvlr/vlr.c
+++ b/src/libvlr/vlr.c
@@ -961,6 +961,9 @@
 {
 	struct vlr_instance *vlr = talloc_zero(ctx, struct vlr_instance);
 	OSMO_ASSERT(vlr);
+
+	/* Some of these are needed only on UTRAN, but in case the caller wants
+	 * only GERAN, she should just provide dummy callbacks. */
 	OSMO_ASSERT(ops->tx_auth_req);
 	OSMO_ASSERT(ops->tx_auth_rej);
 	OSMO_ASSERT(ops->tx_id_req);
@@ -969,6 +972,7 @@
 	OSMO_ASSERT(ops->tx_cm_serv_acc);
 	OSMO_ASSERT(ops->tx_cm_serv_rej);
 	OSMO_ASSERT(ops->set_ciph_mode);
+	OSMO_ASSERT(ops->tx_common_id);
 	OSMO_ASSERT(ops->subscr_update);
 	OSMO_ASSERT(ops->subscr_assoc);