mac80211: combine status/drop reporting

The TX status reporting is done for both the
nl80211 report as well as the socket option.
The socket option is also reported when an
skb is dropped to guarantee that the copy in
the IDR tree is freed and status is reported
to userspace.

However, when a frame is dropped, no nl80211
status is reported. This can cause userspace
to stop making progress while waiting for a
status notification.

Combine the nl80211 and socket option status
reporting into a new function and call it in
both places -- when the status comes in from
the driver and when the skb is dropped.

While at it, also simplify the code in the
nl80211 portion a bit.

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