mac80211: don't sanitize invalid rates

mac80211: don't sanitize invalid rates

commit 5f4e6b2d3c74c1adda1cbfd9d9d30da22c7484fc upstream.

I found this bug while poking around with a pure-gn AP.

Commit:
cfg80211/mac80211: Use more generic bitrate mask for rate control

Added some sanity checks to ensure that each tx rate index
is included in the configured mask and it would change any
rate indexes if it wasn't.

But, the current implementation doesn't take into account
that the invalid rate index "-1" has a special meaning
(= no further attempts) and it should not be "changed".

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>