ssb: implement spurious tone avoidance

commit 46fc4c909339f5a84d1679045297d9d2fb596987 upstream.

And make use of it in b43. This fixes a regression introduced with
49d55cef5b1925a5c1efb6aaddaa40fc7c693335
b43: N-PHY: implement spurious tone avoidance
This commit made BCM4322 use only MCS 0 on channel 13, which of course
resulted in performance drop (down to 0.7Mb/s).

Reported-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>