rt2x00: Fix scheduling while atomic errors in usb drivers

Call rt2x00_config_intf() outside of the spinlock context since
the call will sleep for USB drivers. By using the ieee80211_if_conf
values as arguments we make keep access tp rt2x00_intf thread safe
even without the lock.

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