Can't specify IPv6 DNS servers during installation

In this WireGuard install script, I have the ability to specify 2 DNS servers.

Since my network natively supports IPv6 out of the box, I want to set up WireGuard in the same way.

However, the script doesn't allow me to add the IPv6 addresses of my DNS servers. I tried both the shortened IPv6 version (fd80::25) and the extended version (fd80:0000:0000:0000:0000:0000:0000:0025). The script will not accept the IPv6 address and ask for it again. I also tried to use the IPv6 as the primary IP address too, didn't work either.

It seems that the install script only allows IPv4 for DNS servers. Manually editing the generated client configs with a text editor to have 1 IPv4 DNS server and 1 IPv6 DNS server works just fine.

Example client.conf (manually edited):

```
[Interface]
PrivateKey = XXXXXXXXXXXXXXXXXXXXXXXXXXX=
Address = 10.0.0.2/32,fd80:0:0::2/128
DNS = 10.0.0.25,fd80::25

...
```