IPV6 rotate needs an improvement

Some VPS offers Ipv6/64 or /48 however these are impossible to use all at once without activating them from the control panel. It would take years to activate all possible millions of ipv6 combinations manually.

For the ipv6 rotate instead of using a random address from the 'block' we should be able to define a list of available ipv6 so we can correctly predict its behavior
Old Behavior:
```js
const video = ytdl(url, {IPv6Block: '2001:2::/48'});
```

New Behavior:
```js
const video = ytdl(url, {IPv6Block: ['2001:2:a','2001:2:b','2001:2:c',...]});
```