This converts mwl8k to use the new station
add/remove callbacks instead of using the
old sta_notify callback.

The new callbacks can sleep, so a lot of
code can be removed now.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Acked-by: NLennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>