Move the "finding" of the right BTS into paging.c

Move the secret of how to find the BTS in a LocationArea into
the paging layer. This allows to implement different strategies
without changing other parts. E.g. we might want to try the BTS
were the device was seen last and then try...

There should be no semantic change and things should continue
to work. It is sadly not tested though.
diff --git a/openbsc/src/paging.c b/openbsc/src/paging.c
index f3bdf69..e647b33 100644
--- a/openbsc/src/paging.c
+++ b/openbsc/src/paging.c
@@ -210,8 +210,8 @@
 	paging_remove_request(&req->bts->paging, req);
 }
 
-void paging_request(struct gsm_bts *bts, struct gsm_subscriber *subscr,
-		    int type, gsm_cbfn *cbfn, void *data)
+static void _paging_request(struct gsm_bts *bts, struct gsm_subscriber *subscr,
+			    int type, gsm_cbfn *cbfn, void *data)
 {
 	struct gsm_bts_paging_state *bts_entry = &bts->paging;
 	struct gsm_paging_request *req;
@@ -237,9 +237,25 @@
 		bsc_schedule_timer(&bts_entry->work_timer, 1, 0);
 }
 
+void paging_request(struct gsm_bts *_bts, struct gsm_subscriber *subscr,
+		    int type, gsm_cbfn *cbfn, void *data)
+{
+	struct gsm_bts *bts = NULL;
+
+	do {
+		bts = gsm_bts_by_lac(_bts->network, subscr->lac, bts);
+		if (!bts)
+			break;
+
+		/* Trigger paging */
+		_paging_request(bts, subscr, RSL_CHANNEED_TCH_F, cbfn, data);
+	} while (1);
+}
+
+
 /* we consciously ignore the type of the request here */
-void paging_request_stop(struct gsm_bts *bts, struct gsm_subscriber *subscr,
-			 struct gsm_lchan *lchan)
+static void _paging_request_stop(struct gsm_bts *bts, struct gsm_subscriber *subscr,
+				 struct gsm_lchan *lchan)
 {
 	struct gsm_bts_paging_state *bts_entry = &bts->paging;
 	struct gsm_paging_request *req, *req2;
@@ -256,6 +272,28 @@
 	}
 }
 
+/* Stop paging on all other bts' */
+void paging_request_stop(struct gsm_bts *_bts, struct gsm_subscriber *subscr,
+			 struct gsm_lchan *lchan)
+{
+	struct gsm_bts *bts = NULL;
+
+	do {
+		/*
+		 * FIXME: Don't use the lac of the subscriber...
+		 * as it might have magically changed the lac.. use the
+		 * location area of the _bts as reconfiguration of the
+		 * network is probably happening less often.
+		 */
+		bts = gsm_bts_by_lac(_bts->network, subscr->lac, bts);
+		if (!bts)
+			break;
+
+		/* Stop paging */
+		_paging_request_stop(bts, subscr, NULL);
+	} while (1);
+}
+
 void paging_update_buffer_space(struct gsm_bts *bts, u_int16_t free_slots)
 {
 	bts->paging.available_slots = free_slots;