Activate neutron L2 Gateway extension

Disable l2gw agent by default to prevent unwanted connection attempts to
absent hardware switch (will be emulated/enabled by test suite on demand).

Change-Id: Iaf6da1e0f73f474d6eaee2b15e7613d58b129150
Related-Prod: PROD-18748
diff --git a/classes/cluster/virtual-offline-pike-ovs-dpdk/openstack/control.yml b/classes/cluster/virtual-offline-pike-ovs-dpdk/openstack/control.yml
index 1f8adb0..20d0dea 100644
--- a/classes/cluster/virtual-offline-pike-ovs-dpdk/openstack/control.yml
+++ b/classes/cluster/virtual-offline-pike-ovs-dpdk/openstack/control.yml
@@ -133,6 +133,8 @@
       notification:
         driver: messagingv2
         topics: "notifications,${_param:stacklight_notification_topic}"
+      l2gw:
+        enabled: true
   nova:
     controller:
       networking: dvr