ethtool: add CRC32 as an RSS hash function

CRC32 engines are usually easily available in hardware and generate
OK spread for RSS hash.  Add CRC32 RSS hash function to ethtool API.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>