ath9k: Wake up for RX filter changes

We must make sure the chip is awake when changing the RX filter
parameters. This could have caused problems, e.g., when changing the
interface to promiscuous mode while in sleep mode.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>