allowDNS doesn't work on Linux: `LinuxEthernetTap::setDns` doesn't do anything

I'm trying to enable allowDNS on Ubuntu, and it's not doing anything. No changes to /etc/resolv.conf, nothing.

I dug into the code, and it looks like this is because LinuxEthernetTap::setDns simply is a no-op:

https://github.com/zerotier/ZeroTierOne/blob/185a3a2c76e6bf1b1c0415871f43076638eb007c/osdep/LinuxEthernetTap.hpp#L61

It found some threads online talking about this:

• https://www.reddit.com/r/zerotier/comments/lmei2w/how_do_you_set_up_the_new_dns_feature/
• https://discuss.zerotier.com/t/dns-servers-ignored-on-ubuntu/25231

But I couldn't find any official docs talking about this, so I thought I'd ask here:

1. Is this feature WIP, or intentionally not supported on Linux?
   • I understand that there are lots of ways to do networking and DNS on Linux. Supporting systemd-resolved would work well for a lot of Linux users (myself include). See How to Implement this in Your VPN Software > If managing a corporate VPN for how to configure dns for a specific tld, which would work well with ZT's model.
2. Would you accept a PR adding some logging to LinuxEthernetTap::setDns with some explanation about the state of this? The current behavior is very confusing.