ethtool: Check for vlan etype or vlan tci when parsing flow_rule

When parsing an ethtool flow spec to build a flow_rule, the code checks
if both the vlan etype and the vlan tci are specified by the user to add
a FLOW_DISSECTOR_KEY_VLAN match.

However, when the user only specified a vlan etype or a vlan tci, this
check silently ignores these parameters.

For example, the following rule :

ethtool -N eth0 flow-type udp4 vlan 0x0010 action -1 loc 0

will result in no error being issued, but the equivalent rule will be
created and passed to the NIC driver :

ethtool -N eth0 flow-type udp4 action -1 loc 0

In the end, neither the NIC driver using the rule nor the end user have
a way to know that these keys were dropped along the way, or that
incorrect parameters were entered.

This kind of check should be left to either the driver, or the ethtool
flow spec layer.

This commit makes so that ethtool parameters are forwarded as-is to the
NIC driver.

Since none of the users of ethtool_rx_flow_rule_create are using the
VLAN dissector, I don't think this qualifies as a regression.

Fixes: eca4205f ("ethtool: add ethtool_rx_flow_spec to flow_rule structure translator")
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>