ethtool, ixgbe: Move RX n-tuple mask fixup to ethtool

The ethtool utility does not set masks for flow parameters that are
not specified, so if both value and mask are 0 then this must be
treated as equivalent to a mask with all bits set.  Currently that is
done in the only driver that implements RX n-tuple filtering, ixgbe.
Move it to the ethtool core.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>