OM2000: Allow configuration of CON from VTY

However, we have no code that generates the OM2K CON List attribute.
diff --git a/openbsc/include/openbsc/gsm_data.h b/openbsc/include/openbsc/gsm_data.h
index e3cefe1..a9f9e5e 100644
--- a/openbsc/include/openbsc/gsm_data.h
+++ b/openbsc/include/openbsc/gsm_data.h
@@ -581,6 +581,9 @@
 			struct {
 				struct llist_head conn_groups;
 			} is;
+			struct {
+				struct llist_head conn_groups;
+			} con;
 		} rbs2000;
 	};