gbproxy: Use provided sgsn_idx in f_send_paging_ps_exp_multi()

Change-Id: I89ca4232e71d98936adfc521312b92cba7ef867f
Related: OS#4951
diff --git a/gbproxy/GBProxy_Tests.ttcn b/gbproxy/GBProxy_Tests.ttcn
index dc5756c..9b883c7 100644
--- a/gbproxy/GBProxy_Tests.ttcn
+++ b/gbproxy/GBProxy_Tests.ttcn
@@ -1543,7 +1543,7 @@
 					    ro_integer exp_on_pcu_idx) runs on BSSGP_ConnHdlr
 {
 	var template (present) PDU_BSSGP exp_rx;
-	exp_rx := f_send_paging_ps(p4, 0, true);
+	exp_rx := f_send_paging_ps(p4, sgsn_idx, true);
 
 	/* FIXME: make sure the relevant BVCs/BSS are connected to the ports! */
 	var ro_default defaults := {};