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

Vector I/O high performance network devices

modulename: vector.ko

configname: CONFIG_UML_NET_VECTOR

Linux Kernel Configuration
└─>UML Network Devices
└─>Vector I/O high performance network devices
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This User-Mode Linux network driver uses multi-message send
and receive functions. The host running the UML guest must have
a linux kernel version above 3.0 and a libc version > 2.13.
This driver provides tap, raw, gre and l2tpv3 network transports
with up to 4 times higher network throughput than the UML network
drivers.

source code: