ethtool: Remove unimplemented flow specification types

struct ethtool_rawip4_spec and struct ethtool_ether_spec are neither
commented nor used by any driver, so remove them.  Adjust padding in
the user-visible unions that included these structures.

Fix references to struct ethtool_rawip4_spec in
ethtool_get_rx_ntuple(), which should use struct ethtool_usrip4_spec.

struct ethtool_usrip4_spec cannot hold IPv6 host addresses and there
is no separate structure that can, so remove ETH_RX_NFC_IP6 and the
reference to it in niu.

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