BSC_Tests: fix race conditions in TC_imm_ass_pre_{ts,chan}_ack_dyn_ts

The TC_imm_ass_pre_chan_ack_dyn_ts sporadically fails on Jenkins.
Similar to [1], this is happening because the VTY command setting
the 'immediate-assignment' strategy back to 'post-chan-ack' is
being sent/processed earlier than the CHANnel REQ message.

TC_imm_ass_pre_ts_ack_dyn_ts is likely affected too, also fix it.

Change-Id: I1e38142d29d0fa2946a858eac13319aa05b42aa3
Related: [1] I38cd31041741b69eb15098a089b4d4b6b918ffd4
diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index 8de3dcb..200fd5b 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -11081,9 +11081,6 @@
 	var uint8_t ra := 2;
 	f_ipa_tx(ts_RSL_CHAN_RQD(int2oct(ra, 1), fn));
 
-	/* (set bts 0 cfg back to default) */
-	f_vty_set_imm_ass(BSCVTY);
-
 	/* Expect the dyn TS to deactivate PDCH first */
 	f_exp_ipa_rx(tr_RSL_RF_CHAN_REL(chan_nr));
 	f_ipa_tx(ts_RSL_RF_CHAN_REL_ACK(chan_nr));
@@ -11116,6 +11113,9 @@
 	dt.sccp_conn_id := rx_c_ind.connectionId;
 	BSSAP.send(ts_BSSAP_CONNECT_res(rx_c_ind.connectionId));
 
+	/* (set bts 0 cfg back to default) */
+	f_vty_set_imm_ass(BSCVTY);
+
 	f_sleep(1.0);
 	f_perform_clear_test_ct(dt);
 	f_shutdown_helper();
@@ -11153,9 +11153,6 @@
 	var uint8_t ra := 2;
 	f_ipa_tx(ts_RSL_CHAN_RQD(int2oct(ra, 1), fn));
 
-	/* (set bts 0 cfg back to default) */
-	f_vty_set_imm_ass(BSCVTY);
-
 	/* Expect the dyn TS to deactivate PDCH first */
 	f_exp_ipa_rx(tr_RSL_RF_CHAN_REL(chan_nr));
 
@@ -11189,6 +11186,9 @@
 	dt.sccp_conn_id := rx_c_ind.connectionId;
 	BSSAP.send(ts_BSSAP_CONNECT_res(rx_c_ind.connectionId));
 
+	/* (set bts 0 cfg back to default) */
+	f_vty_set_imm_ass(BSCVTY);
+
 	f_sleep(1.0);
 	f_perform_clear_test_ct(dt);
 	f_shutdown_helper();