Reenable network.dns.disableIPv6

Hey,

disabling network.dns.disableIPv6 will lead to librewolf unable to connect to IPv6 sites. I'm not sure if disabling this option was because of a security issue, but making it able to connect to sites via IPv6 is an advantage for sure.

Please reenable that option. For the time being, I did it in my own config, but it would be nice to see it reenabled project-wide.