Option to specify concurrency value of multiplexing

[linusyang]

Free plan of cloudflare may have limits on websocket connections. It would be better to give users an option to specify concurrency larger than 1.

The explanation of concurrency option can be found at
https://github.com/v2ray/manual/blob/master/en/configuration/mux.md

[Mygod]

LGTM.

If my site uses more concurrent WebSockets connections than Cloudflare expects, what will happen?

Immediately, nothing. Within reason, Cloudflare will allow occasional spikes in usage beyond our guidelines, and we will not apply unnecessary limits.

Repeated spikes or high continued usage will prompt a dialogue: we'll reach out to learn more about your application. Barring abuse or attack, we will not impose limits errors for any application without contacting the customer.

Customers whose usage claims a disproportionate percentage of resources for their current plan level may be asked to upgrade to the plan level that matches their needs.

[linusyang]

@Mygod Yes, I checked this page before. Cloudflare is very generous. 🤣 Multiplexing also may help (a bit) hiding some characteristics.

Some discussion on another plugin:
https://github.com/cbeuw/Cloak
cbeuw/GoQuiet#33

[VictoriaRaymond]

Maybe default to a larger value, say 16?

[linusyang]

I think the design of SS prefers no multiplexing at all:
shadowsocks/shadowsocks-libev#1444

So default value 1 may be more intuitive for most SS users.