realtek: Fix failsafe mode

realtek: Fix failsafe mode

The RTL8380-RTL9300 switches only forward packets when VLAN ID 1 is
configured. Do not use the standard failsafe configuration for DSA
accessing the default port directly, but configure a switch on the lan1
interface instead.

This will add the VLAN ID 1 configuration to the switch:
$ bridge vlan show
port              vlan-id
lan1              1 PVID Egress Untagged
switch            1 PVID Egress Untagged

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit b7ee0786b56d1088c195fe7c1cdb1ad7d20c9245)