Neutron: Added loading ip6_tables kernel module

ip6_tables is needed for HybridFwDriver

Change-Id: I66c50b74a89c046dc59e59dd2422a80e0642ab72

ansible/roles/neutron/tasks/config.yml

 ---
+- name: Load and persist ip6_tables module
+  include_role:
+    role: module-load
+  vars:
+    modules:
+      - {'name': ip6_tables}
+  when: neutron_services | select_services_enabled_and_mapped_to_host | list | intersect([ "neutron-l3-agent", "neutron-linuxbridge-agent", "neutron-openvswitch-agent" ]) | list | length > 0
+
 - name: Setting sysctl values
   become: true
   vars: