mac80211: set STA flag DISABLE_HE if HE is not supported

Up until now, the IEEE80211_STA_DISABLE_HE flag was set only based
on whether the AP has advertised HE capabilities.
This flag should be set also if STA does not support HE
(regardless of the AP support).

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>