BSC_Tests_CBSP: fix f_exp_rsl_etws(): add some guard time

Recently I noticed sporadic CBSP test case failures on Jenkins:

  Timeout waiting for RSL_OSMO_ETWS_CMD (disable)
    BSC_Tests_CBSP.ttcn:1209 BSC_Tests_CBSP control part
    BSC_Tests_CBSP.ttcn:1056 TC_cbsp_emerg_write_bts_cgi_cchan_disable

The related timeout is set to 5.0 seconds in f_exp_rsl_etws(), what
matches the Warning Period IE sent in CBSP WRITE-REPLACE message.

Adding a debug log printing T.read on receipt of RSL_OSMO_ETWS_CMD
reveals that we're cutting it too close: the message arrives just
a few milliseconds before the timeout expires.

  f_exp_rsl_etws(): T := 4.999196s, remaining 0.000804s
  f_exp_rsl_etws(): T := 4.998683s, remaining 0.001317s
  f_exp_rsl_etws(): T := 4.999344s, remaining 0.000656s

Let's increase the timeout value (+0.5s) to avoid sporadic failures.

Change-Id: Ia40a268f9780ffbcfa2bb962d7c1ac25d16193de
diff --git a/bsc/BSC_Tests_CBSP.ttcn b/bsc/BSC_Tests_CBSP.ttcn
index cba8268..1373002 100644
--- a/bsc/BSC_Tests_CBSP.ttcn
+++ b/bsc/BSC_Tests_CBSP.ttcn
@@ -992,7 +992,7 @@
 
 private function f_exp_rsl_etws(integer rsl_idx := 0, boolean enabled) runs on cbsp_test_CT {
 	var template (present) octetstring tr_apdu;
-	timer T := 5.0;
+	timer T := 5.0 + 0.5; /* +0.5s guard */
 
 	if (enabled) {
 		tr_apdu := f_gen_etws_pn(g_cbsp_ser_no, g_cbsp_msg_id);