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>