bsc: Readd the core network code setting

This will instruct the BSC to patch messages and replace
the old network code with the new one.
diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index e26673a..5a51ac6 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -317,6 +317,7 @@
 	net->msc_data->msc_port = 5000;
 	net->msc_data->ping_timeout = 20;
 	net->msc_data->pong_timeout = 5;
+	net->msc_data->core_ncc = -1;
 
 	gsm_net_update_ctype(net);