bsc: Fix TC_chan_act_ack_est_ind_refused()

This test case was incomplete in that it didn't account for a RLL REL
REQ/RESP before RF_CHAN_REL.

Together with OsmoBSC Change-Id
I64a46b5bcd4272e3fa2ff4ee824c2f3fdff6854b, this test now passes.

Change-Id: Ia5af254d4fc572c1d324f70b5ec99d87bdaf9eb9
diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index b65d899..69f072b 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -356,8 +356,7 @@
 	BSSAP.send(ts_BSSAP_DISC_req(rx_c_ind.connectionId, 0));
 
 	/* expect BSC to disable the channel */
-	rx_rsl := f_exp_ipa_rx(0, tr_RSL_MsgTypeD(RSL_MT_RF_CHAN_REL), T3101_MAX);
-
+	f_expect_chan_rel(0, chan_nr);
 	setverdict(pass);
 }