CONFIG_UML_NET_VDE is not available for thedefaultarchitecture x86.
Result is shown for architecture um

VDE transport

modulename: vde.ko

configname: CONFIG_UML_NET_VDE

Linux Kernel Configuration
└─>UML Network Devices
└─>VDE transport
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
This User-Mode Linux network transport allows one or more running
UMLs on a single host to communicate with each other and also
with the rest of the world using Virtual Distributed Ethernet,
an improved fork of uml_switch.

You must have libvdeplug installed in order to build the vde
transport into UML.

To use this form of networking, you will need to run vde_switch
on the host.

For more information, see <http://wiki.virtualsquare.org/>
That site has a good overview of what VDE is and also examples
of the UML command line to use to enable VDE networking.

If you need UML networking with VDE,
say Y.

source code:

depends
CONFIG_NET
CONFIG_UML_NET or  NOT CONFIG_MODVERSIONS