wifi: mac80211_hwsim: Prevent tsf from setting if beacon is disabled

Setting tsf is meaningless if beacon is disabled, so check that beacon
is enabled before setting tsf.

Reported-by:  <syzbot+064815c6cd721082a52a@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=064815c6cd721082a52a


Tested-by:  <syzbot+064815c6cd721082a52a@syzkaller.appspotmail.com>
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Link: https://patch.msgid.link/tencent_3609AC2EFAAED68CA5A7E3C6D212D1C67806@qq.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>