drivers/net/usb/asix.c: Fix unaligned accesses

Using this driver can cause unaligned accesses in the IP layer
This has been fixed by aligning the skb data correctly using the
spare room left over by the 4 byte header inserted between packets
by the device.

Signed-off-by: Neil Jones <NeilJay@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>