reconsider net.ipv4.tcp_sack in ufw's sysctl.conf

[Jamie Strandboge]

Forwarding this from an email report:

"
i installed ufw recently and it caused quite a bit of confusion when my
sysctl settings were being reset. finally i learned about the included
ufw sysctl.conf file. two issues with it:

it's manually resetting net.ipv4.tcp_sack to 1. that's the sysctl that
i was trying to make sure was set to 0. the comment explaining why it
does that references a problem with a very old openbsd version.

i'd very much like to suggest removing this tcp sack line entirely.

second, the comment at the top references /etc/sysctl.conf, which isn't
used anymore. these days systemd just reads /etc/sysctl.d/*.conf
"