Optionally store IMEI in subscriber table

Add VTY config option "store-imei". When it is set, store the IMEI
sent from the VLR with CHECK-IMEI in the database.

Related: OS#2541
Change-Id: I09274ecbed64224f7ae305e09ede773931da2a57
diff --git a/src/hlr.h b/src/hlr.h
index e9cc747..00fa43c 100644
--- a/src/hlr.h
+++ b/src/hlr.h
@@ -51,6 +51,8 @@
 	struct llist_head ussd_routes;
 
 	struct llist_head ss_sessions;
+
+	bool store_imei;
 };
 
 extern struct hlr *g_hlr;