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/include/openbsc/iucs.h b/include/openbsc/iucs.h
new file mode 100644
index 0000000..fb61a5c
--- /dev/null
+++ b/include/openbsc/iucs.h
@@ -0,0 +1,7 @@
+#pragma once
+
+int gsm0408_rcvmsg_iucs(struct gsm_network *network, struct msgb *msg,
+			uint16_t *lac);
+
+struct gsm_subscriber_connection *subscr_conn_lookup_iu(struct gsm_network *network,
+							struct ue_conn_ctx *ue);