Before MySQL Server can accept IPv6 connections, the operating system on your server host must support IPv6. As a simple test to determine whether that is true, try this command:
$> ping6 ::1 16 bytes from ::1, icmp_seq=0 hlim=64 time=0.171 ms 16 bytes from ::1, icmp_seq=1 hlim=64 time=0.077 ms ...
To produce a description of your system's network interfaces, invoke ifconfig -a and look for IPv6 addresses in the output.
If your host does not support IPv6, consult your system documentation for instructions on enabling it. It might be that you need only reconfigure an existing network interface to add an IPv6 address. Or a more extensive change might be needed, such as rebuilding the kernel with IPv6 options enabled.
These links may be helpful in setting up IPv6 on various platforms: