Correct input_sta "assertion" checks. CTS/ACK CTRL frames are shorter
then sizeof(struct ieee80211_frame_min) and were thus running into the
is_rx_tooshort error case.
Use ieee80211_anyhdrsize() to handle this better but make sure we do
at least have the first 2 octets needed for that.
While here move the safety checks before any code which may not obey
them later, just for good style.

The non-scanning check further down assumes a frame format also not
matching control frames. For now skip the checks for control frames
which allows us to deal with some of them at least now.
We should probably add extra checks for them but I am still contemplating
if this can (or should be) done in a more generic way.

Sponsored by: The FreeBSD Foundation
Obtained from: 20210906 wireless v0.91 code drop
MFC after: 1 week