usb-storage: Add US_FL_IGNORE_DEVICE flag; ignore ZyXEL G220F

This patch adds a new unusual_devs flag for when usb-storage needs to ignore
a device that it would otherwise claim.

We need to ignore the ZyXEL G220F as it is a virtual CDROM drive which
includes the windows driver for this USB-WLAN adapter. After the windows
driver is installed on a windows system, it converts it into a WLAN adapter
(by ejecting the virtual disc).

The virtual CDROM is of no interest to Linux users. The zd1211rw driver will
automatically perform the eject operation, we just need to ensure that
usb-storage does not claim the device.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Phil Dibowitz <phil@ipom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>