BTS_Tests: enlarge Tguard for TC_acch_overpower_rxqual_thresh

With recent osmocom-bb.git patches [1][2][3] this testcase needs
slightly more time to execute all 8 TopTestCase steps.

Change-Id: Ia693e91b2bcf71cac0bcda07124ab99e97d27dcd
Related: [1] Ia42550d5c2d8b49efbdf8ef0ce46b26afd1c464e
Related: [2] Ic8a5b6277c6b16392026e0557376257d71c9d230
Related: [3] I838b1ebc54e4c5d116f8af2155d97215a6133ba4
diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index fa4e426..fddfcca 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -8765,7 +8765,8 @@
 	};
 
 	pars := valueof(t_Pars(t_RslChanNr_Bm(0), ts_RSL_ChanMode_SIGN,
-			       spec := { top := top }, trx_nr := 1));
+			       spec := { top := top }, trx_nr := 1,
+			       t_guard := 30.0));
 	vc_conn := f_start_handler(refers(f_TC_acch_overpower), pars);
 	vc_conn.done;