The comment module is compiled out on several embedded systems (and
also gentoo, because netfilter can't go brrrr with comments holding it
back). Attempting to use comments results in a confusing error, and a
non-functional firewall.
Additionally, make the legacy rule cleanup non-fatal, because we *do*
have to probe for the existence of these -m comment rules, and doing
so will error out on these systems.
Signed-off-by: David Anderson <danderson@tailscale.com>