util/linuxfw: fix broken tests

These tests were broken at HEAD. CI currently does not run these
as root, will figure out how to do that in a followup.

Updates #5621
Updates #8555
Updates #8762

Signed-off-by: Maisem Ali <maisem@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f