ieee802154/atusb: Mark driver as AACK enabled in hardware.

Since firmware version 0.2 we use AACK handling directly in the firmware.
Inform the stack that the hardware supports and uses it.

Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>
Acked-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>