mac80211: set BSS_CHANGED_IDLE on vif reconfig

The vif might be busy while reconfiguring
(e.g. associated), so indicate BSS_CHANGED_IDLE as well.

Reported-by: Eyal Shapira <eyal@wizery.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>