dt-bindings: net: dsa: document felix family in dsa-tag-protocol

dt-bindings: net: dsa: document felix family in dsa-tag-protocol

The Vitesse/Microsemi/Microchip family of switches supported by the
Felix DSA driver is capable of selecting between the native tagging
protocol and ocelot-8021q. This is necessary to enable flow control on
the CPU port.

Certain systems where these switches are integrated use the switch as a
port multiplexer, so the termination throughput is paramount. Changing
the tagging protocol at runtime is possible for these systems, but since
it is known beforehand that one tagging protocol will provide strictly
better performance than the other, just allow them to specify the
preference in the device tree.

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