CONFIG_INET6_TUNNEL (not configurable)

modulename: tunnel6.ko

configname: CONFIG_INET6_TUNNEL

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>The IPv6 protocol
└─>INET6_TUNNEL
In linux kernel since version 2.6.12  
source code:
net/ipv6/tunnel6.c