Remove redundancy in LAC processing

Always use LAC which is part of Cell Global ID otherwise we might end up
in a situation where separately stored LAC differs.

Both are described in 3GPP TS 23.008 $2.4 as temporary subscriber data
to be stored in VLR. Both are defined in 3GPP TS 23.003. The LAC is part
of LAI which is part of CGI so there should be no case when those values
differ for a given subscriber.

Change-Id: I993ebc3e14f25e83124b6d3f8461a4b18f971f8e
diff --git a/src/libmsc/gsm_09_11.c b/src/libmsc/gsm_09_11.c
index 43bf48c..3ee6e92 100644
--- a/src/libmsc/gsm_09_11.c
+++ b/src/libmsc/gsm_09_11.c
@@ -287,7 +287,7 @@
 	}
 
 	/* If subscriber is not "attached" */
-	if (!vsub->lac) {
+	if (!vsub->cgi.lai.lac) {
 		LOGP(DMM, LOGL_ERROR, "Network-originated session "
 			"rejected - subscriber is not attached\n");
 		return NULL;