disable default dhcpv6-client firewall rule

none of our hosts are configured using dhcpv6 so no need to allow this
default firewall hole to remain in place.

roles/firewalld/tasks/main.yml

@@ -10,3 +10,10 @@
     name: firewalld
     enabled: "{{configure_firewall}}"
     state: "{{configure_firewall | ternary('started', 'stopped') }}"
+
+- name: disable default dhcpv6-client rule
+  firewalld:
+    service: dhcpv6-client
+    state: disabled
+    immediate: yes
+  when: configure_firewall