This doesn't make any sense since we are expected to be on
the medium or at least to Tx only when we are on the right
channel and the AP/GO can hear us.

Move the call to mgd_prepare_tx() for deauth to be only
done in case we're sending a deauth while not associated.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>