base / iptables: don't try and disable ip6tables on rhel8 with nftables

rhel8 instances using nftables don't have iptables-services installed,
because we remove 'iptables'. On rhel9 and fedora iptables-services only
needs iptables-libs installed, so it's there and works to disable.

Once the last things (rhel8 copr hypervisors) are moved to nftables, we
can drop all this.

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

roles/base/tasks/main.yml

@@ -366,6 +366,7 @@
   when:
   - baseiptables|bool
   - nftables
+  - ansible_distribution_major_version|int > 8
 
 - name: Enable journald persistence
   ansible.builtin.file: path=/var/log/journal state=directory