mac80211: simplify wmm check during association

Instead of setting assoc_data->wmm_used solely
based on the BSS also take into account our own
capabilities and later check those.

Also rename "wmm_used" and "uapsd_used" to just
"wmm" and "uapsd".

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>