DNS and Hostname setup fixes and tweaks

I could not figure out how to create a pr for the commits separately.

These 5 commits:
1. fix broken dns when configuring IPv6 -> ipnotes also needs to be: files dns
2. SetHostname also updates /etc/hosts, make the system boot cleanly (no warning spam or very long delay on login) when booting without a network connection
3. Automaticaly set host name based on mac + prefix
4. More flexible DNS configuration options, supports multiple name servers (IPv6 Dual stack support)
5. Turn UseDNS into a wrapper for backwards compatibility