rt2x00: implement reconfig_complete

mac80211 has .reconfig_complete that can be used as indicator of
HW restart end. This will allow to configure keys/IV differently
for HW restart and normal configuration.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>