First, I say my situation to you.
My LEDE device on RPi3 have 1 Embedded WLAN, 1 Embedded Eth, 1 USB-LTE Modem and 3 RTL8152 Eth.
Yes, It's verrry funny sutuation but I have purposefully set up.
This is a test for one experiment.
Embedded Ethernet is eth0 and WAN.
Embedded WLAN is wlan0 and lan.
LTE Moden is usb0 and wwan.
Last, 3 RTL8152 are eth1, eth2, eth3 and lan.
I installed kmod-usb-net-rtl8152.
this img is my lan config
But there is a problem here.
DHCP doesn't work eth1~3.
Static IP doesn't work, too.
I don't know how to Multi-LAN.
Please let me know what I missed.