Change docker_gwbridge subnet

Change-Id: Ibcedd2dce7a117e2cf96c4379c156d54aaec0299
diff --git a/docker/swarm/worker.yml b/docker/swarm/worker.yml
index acdb0cf..643b207 100644
--- a/docker/swarm/worker.yml
+++ b/docker/swarm/worker.yml
@@ -1,4 +1,8 @@
+classes:
+  - system.docker.swarm.network.gwbridge
 parameters:
+  _param:
+    docker_gwbridge_subnet: 10.20.0.0/16
   docker:
     swarm:
       role: worker