Mailcow: Remove any traces of IPv6.

In the Kata container pod that is used to run Mailcow, ip6tables fails
with messages such as:

    ipv6nat-mailcow_1    running [/sbin/ip6tables -t filter -S --wait]: exit status 3: ip6tables v1.8.4 (legacy): can't initialize ip6tables table `filter': Table does not exist (do you need to insmod?)
    ipv6nat-mailcow_1    Perhaps ip6tables or your kernel needs to be upgraded.

This is causing the Netfilter service to fail, breaking fail2ban.
2 files changed
tree: 8fc2891bf8aa47805fb62ba5e734e25452fb0aa8
  1. forks/
  2. mailcow/
  3. tikiwiki/
  4. images.nix
  5. makefile