mac80211: fix struct ieee80211_tx_queue_params

Multiple issues:
 - there are no "default" values needed
 - cw_min/cw_max can be larger than documented
 - restructure to decrease size
 - use get_unaligned_le16

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