sgsn: replace variable bssgp with ran_index

Since bssgp also been used for Iu connection,
rename the variable to ran_index.
Be consistent and use the same variable name everywhere.

Change-Id: Ib278410bc49f07387873740ed8b411a815d940a8
diff --git a/sgsn/SGSN_Tests_Iu.ttcn b/sgsn/SGSN_Tests_Iu.ttcn
index 472774e..786961f 100644
--- a/sgsn/SGSN_Tests_Iu.ttcn
+++ b/sgsn/SGSN_Tests_Iu.ttcn
@@ -66,7 +66,7 @@
 	f_gmm_attach(umts_aka_challenge := true, force_gsm_sres := false, ran_index := 0);
 
 	/* do a routing area update */
-	f_routing_area_update(g_pars.ra, bssgp := 3);
+	f_routing_area_update(g_pars.ra, ran_index := 3);
 	setverdict(pass);
 }