net: mscc: ocelot: support matching on EtherType

Currently, the filter's protocol is ignored except for a few special
cases (IPv4 and IPv6).

The EtherType can be matched inside VCAP IS2 by using a MAC_ETYPE key.
So there are 2 cases in which EtherType matches are supported:

  - As part of a larger MAC_ETYPE rule, such as:

    tc filter add dev swp0 ingress protocol ip \
            flower skip_sw src_mac 42:be:24:9b:76:20 action drop

  - Standalone (matching on protocol only):

    tc filter add dev swp0 ingress protocol arp \
            flower skip_sw action drop

As before, if the protocol is not specified, is it implicitly "all" and
the EtherType mask in the MAC_ETYPE half key is set to zero.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>