nl80211: Add TX queue parameter configuration

Add a new attribute, NL80211_ATTR_WIPHY_TXQ_PARAMS, that can be used with
NL80211_CMD_SET_WIPHY for userspace (e.g., hostapd) to set TX queue
parameters (txop, cwmin, cwmax, aifs).

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>