OM2000: Allow configuration of CON from VTY

However, we have no code that generates the OM2K CON List attribute.
diff --git a/openbsc/src/gsm_data.c b/openbsc/src/gsm_data.c
index 395339e..3a53220 100644
--- a/openbsc/src/gsm_data.c
+++ b/openbsc/src/gsm_data.c
@@ -578,6 +578,7 @@
 		break;
 	case GSM_BTS_TYPE_RBS2000:
 		INIT_LLIST_HEAD(&bts->rbs2000.is.conn_groups);
+		INIT_LLIST_HEAD(&bts->rbs2000.con.conn_groups);
 		break;
 	}