msc: fix 2 Iu tests: use f_mm_common() instead of f_mm_auth()

Fix these tests by using f_mm_common(), which takes care of Iu auth+ciph:
TC_iu_lu_imsi_reject
TC_iu_lu_imsi_timeout_gsup

Change-Id: Id2bf160ac4e1cad4770202c6a6f1b8eeeee21d68
diff --git a/msc/MSC_Tests.ttcn b/msc/MSC_Tests.ttcn
index 480ec96..6e482e2 100644
--- a/msc/MSC_Tests.ttcn
+++ b/msc/MSC_Tests.ttcn
@@ -478,7 +478,7 @@
 
 	f_create_gsup_expect(hex2str(g_pars.imsi));
 	f_cl3_or_initial_ue(l3_lu);
-	f_mm_auth();
+	f_mm_common();
 	GSUP.receive(tr_GSUP_UL_REQ(g_pars.imsi));
 	GSUP.send(ts_GSUP_UL_ERR(g_pars.imsi, 23));
 	alt {
@@ -508,7 +508,7 @@
 
 	f_create_gsup_expect(hex2str(g_pars.imsi));
 	f_cl3_or_initial_ue(l3_lu);
-	f_mm_auth();
+	f_mm_common();
 	GSUP.receive(tr_GSUP_UL_REQ(g_pars.imsi));
 	/* Normally the HLR would need to respond here, but we decide to force a timeout here */
 	alt {