lchan: Create a structure for MSC data of the lchan

Prepare to split the BSC and the MSC part by putting the
MSC data for a connection into a "gsm_subscriber_connection"
struct and renaming the macros.
diff --git a/openbsc/src/bsc_rll.c b/openbsc/src/bsc_rll.c
index 1551d94..9a4f5aa 100644
--- a/openbsc/src/bsc_rll.c
+++ b/openbsc/src/bsc_rll.c
@@ -51,8 +51,11 @@
 
 static void complete_rllr(struct bsc_rll_req *rllr, enum bsc_rllr_ind type)
 {
+	struct gsm_subscriber_connection *conn;
+
+	conn = &rllr->lchan->conn;
 	llist_del(&rllr->list);
-	put_lchan(rllr->lchan);
+	put_subscr_con(conn);
 	rllr->cb(rllr->lchan, rllr->link_id, rllr->data, type);
 	talloc_free(rllr);
 }
@@ -70,6 +73,7 @@
 			     enum bsc_rllr_ind),
 		  void *data)
 {
+	struct gsm_subscriber_connection *conn;
 	struct bsc_rll_req *rllr = talloc_zero(tall_bsc_ctx, struct bsc_rll_req);
 	u_int8_t link_id;
 	if (!rllr)
@@ -83,7 +87,8 @@
 	     lchan->type == GSM_LCHAN_TCH_H) && sapi != 0)
 		link_id |= 0x40;
 
-	use_lchan(lchan);
+	conn = &lchan->conn;
+	use_subscr_con(conn);
 	rllr->lchan = lchan;
 	rllr->link_id = link_id;
 	rllr->cb = cb;