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.

Sponsored by:	The FreeBSD Foundation
Obtained from:	20210906 wireless v0.91 code drop
MFC after:	3 days
Reviewed by:	adrian
Differential Revision: https://reviews.freebsd.org/D32238