rt2x00: Remove ieee80211_bss_conf from rt2x00_intf

We can safely remove ieee80211_bss_conf from rt2x00_intf,
it is provided by mac80211 in ieee80211_vif as well.
(rt2x00_intf is the drv_priv field of ieee80211_vif).

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>