Transformation virtual interface

modulename: xfrm_interface.ko

configname: CONFIG_XFRM_INTERFACE

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Transformation virtual interface
In linux kernel since version 3.10 (release Date: 2013-06-30)  
This provides a virtual interface to route IPsec traffic.

If unsure, say N.

source code:
net/xfrm/