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/libcommon/debug.c b/src/libcommon/debug.c
index dc79a84..7dbbc6a 100644
--- a/src/libcommon/debug.c
+++ b/src/libcommon/debug.c
@@ -184,6 +184,11 @@
 		.description = "Visitor Location Register",
 		.enabled = 1, .loglevel = LOGL_DEBUG,
 	},
+	[DIUCS] = {
+		.name = "DIUCS",
+		.description = "Iu-CS Protocol",
+		.enabled = 1, .loglevel = LOGL_DEBUG,
+	},
 };
 
 static int filter_fn(const struct log_context *ctx, struct log_target *tar)