lantiq-xrx200: fix wan LED on o2 box 6431

lantiq-xrx200: fix wan LED on o2 box 6431

The WIFI LED already worked for me with the latest openwrt 22.03 version.
Wifi LED did not with an older 22.x version (in gluon - there phy0radio did nothing but phy0tpt did show activity

the WAN interface has the name "wan" and not "pppoe-wan" on this device

fixes #7757 (and FS#2987)

Signed-off-by: Florian Maurer <f.maurer@outlook.de>
(cherry picked from commit 0820d620123a03b6db6642acb6e950d22ffb030f)
Signed-off-by: Jan-Niklas Burfeind <git@aiyionpri.me>