Enable port_security by default

Neutron recommend as good practice to enable port_security
extension by default. Current networks will remain using
security groups, but will allow users to disable port_security
in their port or networks.
An example use case is nfv.

Change-Id: I69f2e3567fd00695cf1c4bcc9177c2b88e33c3ab

ansible/roles/neutron/defaults/main.yml

@@ -254,7 +254,7 @@ extension_drivers:
   - name: "qos"
     enabled: "{{ enable_neutron_qos | bool }}"
   - name: "port_security"
-    enabled: "{{ enable_tacker | bool or enable_designate | bool }}"
+    enabled: true
   - name: "dns"
     enabled: "{{ enable_designate | bool }}"
 

releasenotes/notes/enable_port_security_extension-dfadfe9b288a49d2.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - |
+    Neutron port_security extension driver is enabled by default.