autotest: Fix network_WiFi_IBSS by increasing timeout

This test will pass on lumpy repeatedly now.  We consistently find the
IBSS network beacon at exactly 15.93 seconds on lumpy, which indicates
that the router is consistently taking a while send beacons.

BUG=chromium:265684
TEST=This test passes repeatedly now.

Change-Id: Ie24e8592774afd07065fc98ebf8cf9f7a4cd06ed
Reviewed-on: https://gerrit.chromium.org/gerrit/65253
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
1 file changed