Add support for IPv4 ARP filtering in the driver. This will dramatically
reduce the number of unnecessary interrupts by the device in conqested
networks.

This patch is based on a similar patch to wl1251 by Janne Ylälehto.

Cc: Janne Ylälehto <janne.ylalehto@nokia.com>
Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>