ethtool: Compat handling for struct ethtool_rxnfc

This structure was accidentally defined such that its layout can
differ between 32-bit and 64-bit processes.  Add compat structure
definitions and an ioctl wrapper function.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: stable@kernel.org [2.6.30+]
Signed-off-by: David S. Miller <davem@davemloft.net>