mac80211: set wifi_acked[_valid] bits for transmitted SKBs

There may be situations in which the in-kernel originator of an
SKB cares about its wifi transmission status. To have that, set
the wifi_acked[_valid] bits before freeing/orphaning the SKB if
the destructor is set. The originator can then use it in there.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>