mwifiex: Add support for auto ARP in mwifiex.

This patch adds support for auto ARP feature in mwifiex.
The device will respond to ARP requests from the network
with ARP response in suspended state without waking up the host.
This feature is enabled in the driver by default.

Signed-off-by: Maithili Hinge <maithili@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>