nfp: add ethtool flow steering callbacks

nfp: add ethtool flow steering callbacks

This is the first part to implement flow steering. The communication
between ethtool and driver is done. User can use following commands
to display and set flows:

ethtool -n <netdev>
ethtool -N <netdev> flow-type ...

Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20231117071114.10667-2-louis.peens@corigine.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>