mac80211: fix crash with P2P Device returning action frames

If a P2P Device interface receives an unhandled action
frame, we attempt to return it. This crashes because it
doesn't have a channel context. Fix the crash by using
status->band and properly mark the return frame as an
off-channel frame.

Reported-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>