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 <[email protected]>

target/linux/realtek/base-files/lib/preinit/05_set_preinit_iface_realtek

@@ -0,0 +1,13 @@
+set_preinit_iface() {
+
+	# Create a switch on lan1 to configure the VLAN 1.
+	# Without configuring VLAN ID 1 RTL8380 - RTL9300 will not
+	# forward packets.
+	ip link add name switch type bridge vlan_filtering 1
+	ip link set dev lan1 master switch
+	ip link set lan1 up
+
+	pi_ifname=switch
+}
+
+boot_hook_add preinit_main set_preinit_iface

target/linux/realtek/base-files/lib/preinit/98_remove_preinit_realtek

@@ -0,0 +1,6 @@
+remove_switch() {
+	# delete switch created in 05_set_preinit_iface_realtek again
+	ip link del name switch
+}
+
+boot_hook_add preinit_main remove_switch