modulename: nf_nat_ipv6.ko

configname: CONFIG_NF_NAT_IPV6

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>The IPv6 protocol
└─>IPv6: Netfilter Configuration
└─>IPv6 NAT
In linux kernel since version 3.1 (release Date: 2011-10-24)  
The IPv6 NAT option allows masquerading, port forwarding and other
forms of full Network Address Port Translation. This can be
controlled by iptables or nft.

source code: