mac80211: recalculate idle later in MLME

hwsim testing has revealed that when the MLME
recalculates the idle state of the device, it
sometimes does so before sending the final
deauthentication or disassociation frame. This
patch changes the place where the idle state
is recalculated, but of course driver transmit
is typically asynchronous while configuration
is expected to be synchronous, so it doesn't
fix all possible cases yet.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>