wifi: mac80211_hwsim: drop short frames

While technically some control frames like ACK are shorter and
end after Address 1, such frames shouldn't be forwarded through
wmediumd or similar userspace, so require the full 3-address
header to avoid accessing invalid memory if shorter frames are
passed in.

Reported-by:  <syzbot+b2645b5bf1512b81fa22@syzkaller.appspotmail.com>
Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>