mediatek: fix WLAN LED indication for ipTIME AX3000SE

mediatek: fix WLAN LED indication for ipTIME AX3000SE

OpenWrt has recently added the "network" LED trigger to support routers
that have a single WLAN LED for multiple phys.

This patch replaces the temporary workaround used during initial
support, where the LED was triggered only by activity on a single phy.

With this change, the WLAN LED on the ipTIME AX3000SE now correctly
indicates activity on both `phy0` and `phy1`.

Signed-off-by: Donghyun Ko <nyankosoftware@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23723
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>