net: dsa: mv88e6xxx: enable set_policy

Enabling set_policy capability for mv88e6321.

Signed-off-by: Angelo Dureghello <angelo.dureghello@timesys.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20221110091027.998073-1-angelo.dureghello@timesys.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>