Before submitting your PR, please review the following checklist:

• CHOOSE CORRECT BRANCH: if filing a bugfix/enhancement
  against certain release version, choose 0.9, 0.10 or 0.11 branch,
  for dev-edition use master branch
• CONSIDER adding a unit test if your PR resolves an issue
• LIST ISSUES this PR resolves
• MAKE SURE this PR doesn't break existing tests
• KEEP PR small so it could be easily reviewed.
• AVOID making unnecessary stylistic changes in unrelated code
• ACCOMPANY each new failregex for filter X with sample log lines
  within fail2ban/tests/files/logs/X file

XDPDropper action

Adding a new action that allows to ban clients via eBPF XDP, resulting in more efficient packet dropping.
Ideally, this would be better than nftables ingress hook in case of DDOS attacks.

This action requires a configured instance of XDPDropper. For Arch Linux users, I created an easy to install package in the AUR, that should be trivial to adapt to other distros.

References:

• https://github.com/renanqts/xdpdropper
• https://aur.archlinux.org/packages/xdpdropper
• https://blog.cloudflare.com/how-to-drop-10-million-packets/
• https://wiki.nftables.org/wiki-nftables/index.php/Nftables_families