mac80211: deprecate qual value

mac80211: deprecate qual value

This value is unused by mac80211, because it was only
be used by wireless extensions, and turned out to not
be useful there because the quality value needs to be
comparable between scan results and the current value
which is impossible when the qual value is calculated
taking into account noise, for example.

Since it is unused anyway, this patch deprecates it
in the hope that drivers will remove their sometimes
quite expensive calculations of the value.

I'm open to actual uses of the value, but the best
way of using it seems to be what the Intel drivers do
which should probably be generalised if we have noise
values from the hardware.

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