netdev: usb: dm9601.c can drive a device not supported yet, add support for it

I found that the current version of drivers/net/usb/dm9601.c can be used to
successfully drive a low-power, low-cost network adapter with USB ID
0a46:9000, based on a DM9000E chipset. As no device with this ID is yet
present in the kernel, I have created a patch that adds support for the device
to the dm9601 driver.

Created and tested against linux-2.6.32-rc5.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>