cherry-pick Xiaomi AC2350 for 21.02

[Simon Iremonger]

Dear All,


I would like commit  6c148116f778bfd2db88476cee4753b32538eafe
cherry-picked into  21.02 branch, having thoroughly tested
this works on the  Xiaomi AC2350  router.

This is a very simple backport, devicetree and device-script,
all well supported components already.


I have tested cherry-picking this in 21.02 from git and building
21.02-SNAPSHOT r16335+1-4b0f87729c  image and tested it on
extensively on the AC2350 as best we can!.


We have tested all we can:-

* 2.4ghz wifi
* 5ghz wifi
* Ethernet Switch config, matches up with physical labels
* Reset button works
* LEDs (2 different 2 colour LEDs) work exactly as described
* 1508 mini Jumbo on Wan with 1500MTU PPPoE-WAN.
* Works fine for 2 weeks
* IPv6 working (did not test turning on flow offloading,
     a known current issue anyhow).

Kept activity up, speed tests, port forwarding, streaming,
no apparent issues!.


Happy to provide more information, but in short I am
confident  6c148116f778bfd2db88476cee4753b32538eafe
is ready to cherry-pick so  Xiaomi-AC2350 can be in
21.02.2 and onwards.


With many thanks

--Simon