Upgrade OpenWrt from 18.06.4 to 19.07.1

OpenWrt 19.07 is the latest stable release, and 18.06 is being legacy. I use 18.06 great except sometime WiFi is not available, very few times.

My router is Linksys WRT 1900AC v2.

According official document, I could upgrade 18.06 to 19.07, document said for many cases, I backed up configurations and flash the sysupgrade image, everyting works fine, and after router started up, my networking still recovered without my custom softwares.

I installed Shadowsocks stack (shadowsocks, chinadns, dns-forwarder), and luci apps, but their luci apps crashed, missing cbi.lua, it's a known issue, just install luci-compat.

I didn't setup WiFi country code properly before, I used US, every country's WiFi available frequency is different, and you should set it where your router in, so I should set it CN as I'm living in China now.

I modified 5G WiFi channel to auto, maybe it's not a good choice, as auto is just a shorthand for first available channel, not a dynamic channel? I'm not sure, so I just pick up one available channel in China, current I use 149, and width 80MHz.

I dropped support for legacy 802.11b rates as I still closed 2.4GHz WiFi.

I have no knowledge to tuning WiFi distance optimization, so just level blank.

After I upgrade router, I tested performance via iperf3, I setup iperf3 server on NAS and client on mobile phone, on MacBookPro, the results:

no additional increments...