change to native ansible iptables flush

  register: boot_cmdline

- name: Flush iptables before changing iptables-legacy

  shell:

    cmd: 'iptables -F'

  register: flush_iptables

  changed_when:

    - flush_iptables.rc == 0 and flush_iptables.stdout_lines.count == 0

  iptables:

    flush: true

  when:

    - ansible_facts.distribution_release is search("buster")