lib/neutron: Add port_security ml2 extension driver

Tempest currently conducts tests for this extension driver by
default.

Change-Id: I5f9881d0713965b66358dc9cade8d623da98d75d
diff --git a/lib/neutron b/lib/neutron
index ad68d8e..22584c6 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -166,6 +166,7 @@
         iniset $NEUTRON_PLUGIN_CONF ml2 type_drivers vxlan
         iniset $NEUTRON_PLUGIN_CONF ml2 mechanism_drivers openvswitch,linuxbridge
         iniset $NEUTRON_PLUGIN_CONF ml2_type_vxlan vni_ranges 1001:2000
+        iniset $NEUTRON_PLUGIN_CONF ml2 extension_drivers port_security
     fi
 
     # Neutron OVS or LB agent