ath9k: Fix rx filtering issue for older chips

We need to have the promiscuous mode enabled for older
chipsets so that the olderchips hardware does not
filters out some valid/necessary frames that need
to be sent to mac80211. Fix this by enabling promiscus
mode for all the chipsets whose macversion <= AR9160
chipsets. This should fix
https://bugzilla.kernel.org/show_bug.cgi?id=45591

shafi: made the fix generic by having the frame filtering
disabled for chipsets older than AR9280.

Cc: Javier Cardona <javier@cozybit.com>
Signed-off-by: Thomas Wagner <Thomas.Wagner@hs-rm.de>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>