mac80211: Add WME information element for IBSS

Enable WME QoS in IBSS mode by adding a WME information element to beacons and
probe respones and by checking for it and marking stations as WME capable if it
is present.

Signed-off-by: Bruno Randolf <br1@einfach.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>