Set IP_VERSION default value to 4+6

This is actually the default value since 645114b

Change-Id: Ib6603b4f6ea0b4079f9a4ea46e723ecbb2ea371d
diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index 1cc7083..8e2e7ff 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -391,7 +391,7 @@
         ENABLED_SERVICES=n-vol,n-cpu,n-net,n-api
 
 IP Version
-    | Default: ``IP_VERSION=4``
+    | Default: ``IP_VERSION=4+6``
     | This setting can be used to configure DevStack to create either an IPv4,
       IPv6, or dual stack tenant data network by setting ``IP_VERSION`` to
       either ``IP_VERSION=4``, ``IP_VERSION=6``, or ``IP_VERSION=4+6``