mac80211: mlme: add documentation from spec to code

Reference the spec why we decline HE support in
case STA don't support all HE basic rates recurred by AP.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220202104617.f1bafd0861b7.I566612d99bca5245dc06cbcc70369b94a525389c@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>