fail2ban: Use a managed firewalld ipset

The firewalld direct interface is deprecated and will be removed in a future release[1]. Recently IPv4 connectivity inside docker containers on our runners broke and after some troubleshooting, the issue was pinpointed to the start of the fail2ban service. We also had issues in the past where sometimes firewalld had to be restarted after boot before network connectivity worked in libvirt on our runners.

The issuse may be due to a bug in the way fail2ban use the direct interface, a bug in firewalld or a combination thereof. Let's just avoid the direct interface altogether and create a clean separation, with firewalld handling the blocking and fail2ban maintaining the ipset.

[1] https://firewalld.org/documentation/man-pages/firewalld.direct.html

roles/fail2ban/files/fail2ban.xml

+<?xml version="1.0" encoding="utf-8"?>
+<ipset type="hash:net">
+</ipset>