ath9k: Fix RX Filter handling for BAR

BAR frames have to be sent to mac80211 only if the
current channel is HT. Also, move the macro to
enum ath9k_rx_filter.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>