OpenWrt 21.02.0 Fourth release candidate

[Arınç ÜNAL]

Congrats! Before we get to the final release, the DSA migration script
should be included.
Looks like I'm going to hire someone to write the script for me. I
know DSA, not changing text on configuration files with awk, grep,
etc.
Want to give a hand? Please let me know.

I still plan to update the converting to DSA page here:
https://openwrt.org/docs/guide-user/network/dsa/converting-to-dsa

Cheers.
Arınç