net: ethtool: Allow parsing ETHER_FLOW types when using flow_rule

When parsing an ethtool_rx_flow_spec, users can specify an ethernet flow
which could contain matches based on the ethernet header, such as the
MAC address, the VLAN tag or the ethertype.

ETHER_FLOW uses the src and dst ethernet addresses, along with the
ethertype as keys. Matches based on the vlan tag are also possible, but
they are specified using the special FLOW_EXT flag.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Acked-by: Pablo Neira Ayuso <pablo@gnumonks.org>
Signed-off-by: David S. Miller <davem@davemloft.net>