Setting dev->hard_mtu to 0 will cause a divide error in
usbnet_probe. Protect against devices with bogus CDC Ethernet
functional descriptors by ignoring a zero wMaxSegmentSize.
Signed-off-by: NBjørn Mork <bjorn@mork.no>
Acked-by: NOliver Neukum <oneukum@suse.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>