wl1251: Filter out unwanted events

Filter out unwanted events to reduce wakeups.

Signed-off-by: Janne Ylalehto <janne.ylalehto@nokia.com>
Reviewed-by: Vidhya Govindan <vidhya.govindan@nokia.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>