Add a new chapter about blacklistd to the firewalls chapter.
The most common use case for blacklistd is to add excessive
SSH login attempts to the list of hosts to be blocked. The
user can define when that should happen and how long the IPs
should be listed there. The chapter describes the syntax and
how to set it up.
The examples use PF, but it is possible to use other firewalls
with blacklistd as well.
Reviewed by: kp
Event: EuroBSDcon 2019 Hackathon
Differential Revision: https://reviews.freebsd.org/D20568
UnifiedSplitRaw
