Amount of bytes to Reserve on a skb for the IBM OCP Enet Driver
CONFIG_IBM_OCP_ENET_SKB_RES
  Many standard ethernet drivers need to reserve 2 bytes of data
  on the skb before giving the data ptr to the hardware. This is
  so the IP data will be 16-byte aligned when it goes up the stack.
  This is a requirement for some processors and it can cause major
  slow downs on others. The 405GP dose not have problems with the
  misaligned data so the default is 0. If you need to route the
  incoming ethernet packets to another device that has alignment
  requirements this can help remove a data copy. A value of 2 can
  help at getting 16-byte aligned IP data for another device. A
  larger value can be used when routing to a IP tunnel device.
  Make sure XXX_DESC_SIZE - XXX_SKB_RES >= 1514, or larger if VLANS
  are used.