pcu: TC_dl_multislot_tbf_ms_class_from_sgsn(): Properly wait for USF

Change-Id: I34b31c292c00b6880311906ce6713a8e3c69a0d2
diff --git a/pcu/PCU_Tests.ttcn b/pcu/PCU_Tests.ttcn
index 82ecb57..e381c59 100644
--- a/pcu/PCU_Tests.ttcn
+++ b/pcu/PCU_Tests.ttcn
@@ -3198,6 +3198,7 @@
 	var PacketDlAssign dl_tbf_ass;
 	var RlcmacDlBlock dl_block;
 	var uint32_t poll_fn;
+	var uint32_t dl_fn;
 	var uint32_t sched_fn;
 	var GprsMS ms;
 	timer T := 5.0;
@@ -3224,11 +3225,12 @@
 	f_ms_establish_ul_tbf(ms);
 
 	/* Wait until PCU starts requesting for UL block on this TBF: */
-	f_ms_wait_usf(ms);
+	dl_fn := f_ms_wait_usf(ms, nr := f_ms_tx_TsTrxBtsNum(ms));
+	sched_fn := f_next_pdch_block(dl_fn);
 
 	/* Send one UL block (with TLLI since we are in One-Phase Access
 	   contention resolution) and make sure it is ACKED fine */
-	f_ms_tx_ul_data_block(ms, data, with_tlli := true, fn := ms.ul_tbf.start_time_fn,
+	f_ms_tx_ul_data_block(ms, data, with_tlli := true, fn := sched_fn,
 			      nr := f_ms_tx_TsTrxBtsNum(ms));
 	/* DL ACK/NACK sets poll+rrbp requesting PACKET CONTROL ACK */
 	f_rx_rlcmac_dl_block_exp_ack_nack(dl_block, poll_fn, nr := f_ms_tx_TsTrxBtsNum(ms));