mac80211: trim RX data

The RX data contains the netdev, which is
duplicated since we have the sdata, and the
RX status pointer, which is duplicate since
we have the skb. Remove those two fields to
have fewer fields that depend on each other
and simply load them as necessary.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>