bsc: Rename core_ncc to core_mnc

Struct osmo_msc_data contains int core_ncc, which is actually the
MNC part of the PLMN, not to be confused with the Network Colour
Code.

The following patch renames this field for clarity and consistency
with the standards.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_vty.c b/openbsc/src/osmo-bsc/osmo_bsc_vty.c
index 9a17cd0..8103ffc 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_vty.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_vty.c
@@ -110,9 +110,9 @@
 	if (msc->bsc_key_present)
 		vty_out(vty, " auth-key %s%s",
 			osmo_hexdump(msc->bsc_key, sizeof(msc->bsc_key)), VTY_NEWLINE);
-	if (msc->core_ncc != -1)
+	if (msc->core_mnc != -1)
 		vty_out(vty, " core-mobile-network-code %d%s",
-			msc->core_ncc, VTY_NEWLINE);
+			msc->core_mnc, VTY_NEWLINE);
 	if (msc->core_mcc != -1)
 		vty_out(vty, " core-mobile-country-code %d%s",
 			msc->core_mcc, VTY_NEWLINE);
@@ -261,10 +261,10 @@
 DEFUN(cfg_net_bsc_ncc,
       cfg_net_bsc_ncc_cmd,
       "core-mobile-network-code <1-999>",
-      "Use this network code for the core network\n" "NCC value\n")
+      "Use this network code for the core network\n" "MNC value\n")
 {
 	struct osmo_msc_data *data = osmo_msc_data(vty);
-	data->core_ncc = atoi(argv[0]);
+	data->core_mnc = atoi(argv[0]);
 	return CMD_SUCCESS;
 }