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
1 file changed