[dpdk] Support ovs bridge tagging

Bring in "tag" option for dpdk/ovs bridges
to support vlan-tagged vxlan mode.

Change-Id: I7f1f88233694f2c8b968a6cf55584f32879ec042
diff --git a/README.rst b/README.rst
index 794b56b..8628f80 100644
--- a/README.rst
+++ b/README.rst
@@ -1433,6 +1433,7 @@
             type: dpdk_ovs_bridge
             address: 192.168.50.0
             netmask: 255.255.255.0
+            tag: 101
             mtu: 9000
 
 Linux storage