ramips: fix Xiaomi MiWiFi Mini switch definition

ramips: fix Xiaomi MiWiFi Mini switch definition

Based on OpenWRT Table of Hardware > Xiaomi > Xiaomi Mi WiFi Mini

Switch Ports Defaults:
0, 1: LAN
4: WAN
6: CPU

Port in Web GUI (word printed on bottom of case)
WAN(Internet) map to switch port 4
LAN1(.) map to switch port 1
LAN2(..) map to switch port 0
CPU map to switch port 6

current setting is 1 WAN/ 4 LAN port, fix it.

Signed-off-by: Chih-Wei Chen <changeway@gmail.com>
[rebased after base-files split, fixed commit title]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(backported from commit 3e88ab79b03917bc4b03b34db12edf622bde1de1)