wl12xx: AP-mode - use mac80211 indication about STA WME support

When adding a station, use the information given in the mac80211
populated ieee80211_sta structure to determine if it supports WME.
Provide this information to the FW.

This patch depends on "mac80211: propagate information about
STA WME support down".

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>