CONFIG_NET_IP_TUNNEL (not configurable)

modulename: ip_tunnel.ko

configname: CONFIG_NET_IP_TUNNEL

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>NET_IP_TUNNEL
In linux kernel since version 3.1 (release Date: 2011-10-24)  
source code:
net/ipv4/ip_tunnel.c