wifi: cfg80211/mac80211: check EHT capability size correctly

For AP/non-AP the EHT MCS/NSS subfield size differs, the
4-octet subfield is only used for 20 MHz-only non-AP STA.
Pass an argument around everywhere to be able to parse it
properly.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>