mac80211: clean up set_key callback

The set_key callback now seems rather odd, passing a MAC address
instead of a station struct, and a local address instead of a
vif struct. Change that.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Bob Copeland <me@bobcopeland.com> [ath5k]
Acked-by: Ivo van Doorn <ivdoorn@gmail.com> [rt2x00]
Acked-by: Christian Lamparter <chunkeey@web.de> [p54]
Tested-by: Kalle Valo <kalle.valo@nokia.com> [iwl3945]
Tested-by: Samuel Ortiz <samuel@sortiz.org> [iwl3945]
Signed-off-by: John W. Linville <linville@tuxdriver.com>