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/a_iface.c b/src/libmsc/a_iface.c
index 1f471f9..caf9d4b 100644
--- a/src/libmsc/a_iface.c
+++ b/src/libmsc/a_iface.c
@@ -35,6 +35,14 @@
 	return -1;
 }
 
+int a_page(const char *imsi, uint32_t tmsi, uint16_t lac)
+{
+	LOGP(DMSC, LOGL_ERROR, "Paging to be sent to BSC, but A-interface"
+	     " not implemented: IMSI %s TMSI 0x%08x LAC %u\n",
+	     imsi, tmsi, lac);
+	return -1;
+}
+
 int msc_gsm0808_tx_cipher_mode(struct gsm_subscriber_connection *conn, int cipher,
 			       const uint8_t *key, int len, int include_imeisv)
 {