Allow disabling security groups

For some use cases it might be needed to disable security groups.
For example best DPDK performance can be achieved only with disabled
security groups.

Change-Id: I067fa230c0cc5f8042bc405249f99e09250893ec
diff --git a/metadata/service/control/single.yml b/metadata/service/control/single.yml
index 3be2831..24b5a2f 100644
--- a/metadata/service/control/single.yml
+++ b/metadata/service/control/single.yml
@@ -12,6 +12,7 @@
       fwaas: false
       dns_domain: novalocal
       tunnel_type: vxlan
+      security_groups_enabled: true
       version: ${_param:neutron_version}
       bind:
         address: ${_param:single_address}