msc: Fix ti_flag mistake in f_mt_sms()

The L3 transaction-id in MT-SMS is allocated in the MSC, so any
messages we expect from the MSC must carry c_TIF_ORIG.

Change-Id: I6ea977a7662fdfc9c504f13ac5632ac20a04f522
diff --git a/msc/BSC_ConnectionHandler.ttcn b/msc/BSC_ConnectionHandler.ttcn
index 733daab..8c9b723 100644
--- a/msc/BSC_ConnectionHandler.ttcn
+++ b/msc/BSC_ConnectionHandler.ttcn
@@ -880,7 +880,7 @@
 	BSSAP.send(ts_PDU_DTAP_MO(l3_mo, spars.dlci, true));
 
 	/* expect CP-ACK for CP-DATA(RP-ACK) just sent */
-	l3_mt := tr_ML3_MT_SMS(spars.tid, c_TIF_REPL, tr_CP_ACK_MT);
+	l3_mt := tr_ML3_MT_SMS(spars.tid, c_TIF_ORIG, tr_CP_ACK_MT);
 	BSSAP.receive(tr_PDU_DTAP_MT(l3_mt, spars.dlci));
 
 	deactivate(d);