Fix the path of firewall plugin in kolla-ansible.

The path of firewall plugin in kolla-ansible is wrong.

Change-Id: I979af769d8bc31e3b6373a629e9e090b987d0058
Closes-Bug: #1684459

ansible/roles/neutron/defaults/main.yml

@@ -267,7 +267,7 @@ service_plugins:
     enabled: "{{ neutron_plugin_agent == 'sfc' }}"
   - name: "neutron_lbaas.services.loadbalancer.plugin.LoadBalancerPluginv2"
     enabled: "{{ enable_neutron_lbaas | bool }}"
-  - name: "neutron.services.firewall.fwaas_plugin.FirewallPlugin"
+  - name: "neutron_fwaas.services.firewall.fwaas_plugin.FirewallPlugin"
     enabled: "{{ enable_neutron_fwaas | bool }}"
   - name: "neutron_vpnaas.services.vpn.plugin.VPNDriverPlugin"
     enabled: "{{ enable_neutron_vpnaas | bool }}"