Prevents the "iptables: Chain already exists." error by making sure that
we don't leave any chain on start. The ideal solution is to use
iptables-restore instead, which will do the right job. But this needs to
be changed in NixOS entirely.
Reviewed-by: Aleix Boné <abonerib@bsc.es>
Rodrigo Arias Mallo
27636dc66e