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

VDE transport (obsolete)

modulename: vde.ko

configname: CONFIG_UML_NET_VDE

Linux Kernel Configuration
└─>UML Network Devices
└─>VDE transport (obsolete)
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.

NOTE: THIS TRANSPORT IS DEPRECATED AND WILL BE REMOVED SOON!!! Please
migrate to UML_NET_VECTOR.

If unsure, say N.

source code:

depends
CONFIG_NET
CONFIG_UML_NET
NOT CONFIG_MODVERSIONS