ath9k: add support for 802.11n bonded out AR2427

ath9k: add support for 802.11n bonded out AR2427

This is a backport of of upstream commit:

5ffaf8a361b4c9025963959a744f21d8173c7669

Some single chip family devices are sold in the market with
802.11n bonded out, these have no hardware capability for
02.11n but ath9k can still support them. These are called
AR2427.

Reported-by: Rolf Leggewie <bugzilla.kernel.org@rolf.leggewie.biz>
Tested-by: Bernhard Reiter <ockham@raz.or.at>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>