K 10
svn:author
V 2
kp
K 8
svn:date
V 27
2021-10-06T08:48:04.733879Z
K 7
svn:log
V 478
pf: implement adaptive mode

Use atomic counters to ensure that we correctly track the number of half
open states and syncookie responses in-flight.
This determines if we activate or deactivate syncookies in adaptive
mode.

MFC after:	1 week
Sponsored by:	Modirum MDPay
Differential Revision:	https://reviews.freebsd.org/D32134

(cherry picked from commit bf8637181a2bb81206ff8c685f1632d07b8feb13)

Git Hash:   d23f5f76f56d986008c49c7e74bf78e9cad63aa7
Git Author: kp@FreeBSD.org
END