CONFIG_NET_UDP_TUNNEL (not configurable)

modulename: udp_tunnel.ko

and/or

ip6_udp_tunnel.ko

configname: CONFIG_NET_UDP_TUNNEL

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>NET_UDP_TUNNEL
In linux kernel since version 3.10 (release Date: 2013-06-30)  
source code:
net/ipv4/