net: dsa: b53: implement port isolation supportImplement port isolation support via the Protected Ports register.Protected ports can only communicate with unprotected ports, but notwith each other, matching the expected behaviour of isolated ports.Tested on BCM963268BU.Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>Reviewed-by: Vladimir Oltean <olteanv@gmail.com>Link: https://patch.msgid.link/20251013152834.100169-1-jonas.gorski@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>