ar9170: add Cace Airpcap NX usb_id

This patch adds a new device to ar9170usb.

Reported-by: Mike Kershaw/Dragorn <dragorn@kismetwireless.net>
Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>