IPv6: ESP in TCP encapsulation (RFC 8229)

configname: CONFIG_INET6_ESPINTCP

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>The IPv6 protocol
└─>IPv6: 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/IPv6 sockets.

If unsure, say N.