Describe the bug

On Debian/Ubuntu systems without resolvconf installed, NetBird’s systemd service enters a 4-second self-restart loop:

1. Engine configures DNS for wt0 → resolvconf -a wt0 … returns exit status 99
2. NetBird treats this as fatal, logs stopped NetBird Engine, and actively calls free_netdev()
3. wt0 is destroyed → reconnect → loop repeats
   (Docker images are unaffected because they usually ship resolvconf)

To Reproduce

1. sudo apt install resolvconf
2. sudo systemctl restart netbird
3. ip link show wt0 → interface appears and disappears every 4–5 s
4. journalctl -u netbird -f → endless “stopped NetBird Engine”

Expected behavior

DNS setup failure should be logged only, not fatal.
wt0 should remain up and retry DNS later, not self-stop.

Screenshots / Logs

Nov 19 10:46:39 host netbird[374638]: resolvconf: exit status 99
Nov 19 10:46:39 host netbird[374638]: stopped Netbird Engine
Nov 19 10:46:43 host netbird[374638]: WireGuard interface monitor: interface wt0 deleted: failed to lookup interface: route ip+net: no such network interface, restarting engine