Only when RXD advanced layout is enabled, in some cases
(e.g. ip fragments), the checksum of entire packet will be
calculated and filled in the least significant 16 bits of
the unused addr field.

So refactor out the handling of RX completion checksum: adjust
the location of the checksum in RX descriptor, and use ptype table
to identify whether this kind of checksum is calculated.
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>