mac80211: Ensure off-channel frames don't get queued

Commit 6c17b77b

 (mac80211: Fix tx queue
handling during scans) contains a bug that causes off-channel frames to
get queued when they should be handed down to the driver for transmit.
Prevent this from happening.

Reported-by: Fabio Rossi <rossi.f@inwind.it>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>