mac80211: deprecate RX status noise

The noise value as is won't be used, isn't
filled by most drivers and doesn't really
make a whole lot of sense on a per packet
basis -- proper cfg80211 survey support in
mac80211 will need to be different.

Mark the struct member as deprecated so it
will be removed from drivers.

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