the RATELIMIT kernel option

Hello hackers@,

I've been looking at adding the RACK tcp kernel option, and reading the instructions 
on https://klarasystems.com/articles/using-the-freebsd-rack-tcp-stack/

They mention the RATELIMIT option for some network cards but I can find
no option of that name in LINT/NOTES so am not sure if it works with
just some or all network interfaces or what the tradeoffs are. Can anyone here 
clarify please? or just point me to whatever I need to look at, thanks
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