BTS_Tests: populate SACCH cache in f_TC_ms_pwr_ctrl_{constant,pf_ewma}

There is a time window between activation of a dedicated channel and
receipt of a L1CTL_DATA_REQ with the first RR Measurement Report, in
which the L1 may need to start transmission on Uplink SACCH.

In this case the L1 is using a dummy SACCH block with hard-coded L1
SACCH header values and hard-coded Measurement Results.

Until recently we relied on implementation specific behavior of trxcon
patching the L1 SACCH header in hard-coded dummy SACCH block.  This
behavior was changed, so TC_ms_pwr_ctrl_{constant,pf_ewma} started to
fail.  Let's properly populate the SACCH cache to fix these TCs.

Change-Id: I89eb90815e86db466ea626f4c25f2634c1d942d5
Depends: osmocom-bb.git I0f467fc07cf844cc73465f235b36ba7d00788c9f
Related: OS#5635
diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index 395059a..cbbb297 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -7876,6 +7876,12 @@
 	/* Ensure that 'rx-current' equals 'rx-target' */
 	f_trxc_fake_rssi(mp_uplink_power_target);
 
+	/* Populate SACCH cache with a Measurement Report */
+	L1CTL.send(ts_L1CTL_DATA_REQ_SACCH(g_chan_nr, ts_RslLinkID_SACCH(0),
+					   ts_SacchL1Header(g_pars.l1_pars.ms_power_level,
+							    g_pars.l1_pars.ms_actual_ta),
+					   f_pad_oct('010349'O & '0615004001C0'O, 21, '00'O)));
+
 	/* Establish a dedicated channel */
 	f_est_dchan(more_ies := valueof(ies));
 
@@ -7937,6 +7943,12 @@
 	/* Ensure that 'rx-current' equals 'rx-target' */
 	f_trxc_fake_rssi(mp_uplink_power_target);
 
+	/* Populate SACCH cache with a Measurement Report */
+	L1CTL.send(ts_L1CTL_DATA_REQ_SACCH(g_chan_nr, ts_RslLinkID_SACCH(0),
+					   ts_SacchL1Header(g_pars.l1_pars.ms_power_level,
+							    g_pars.l1_pars.ms_actual_ta),
+					   f_pad_oct('010349'O & '0615004001C0'O, 21, '00'O)));
+
 	/* Establish a dedicated channel */
 	f_est_dchan(more_ies := valueof(ies));