IP: ESP in TCP encapsulation (RFC 8229)

modulename: espintcp.ko

configname: CONFIG_INET_ESPINTCP

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>IP: ESP in TCP encapsulation (RFC 8229)
In linux kernel since version 5.1 (release Date: 2019-05-05)  
Support for RFC 8229 encapsulation of ESP and IKE over
TCP/IPv4 sockets.

If unsure, say N.

source code:
net/xfrm/espintcp.c