mac80211: do not advertise HE cap IE if HE disabled

When disabling HE due to the lack of HT/VHT, do it
at an earlier stage to avoid advertising HE capabilities IE.
Also, at this point, no need to check if AP supports HE, since
it is already checked earlier (in ieee80211_prep_channel).

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>