We already disable dynamic updates by setting DisableDynamicUpdate to 1 for the Tailscale interface.
However, this does not prevent non-dynamic DNS registration from happening when `ipconfig /registerdns`
runs and in similar scenarios. Notably, dns/windowsManager.SetDNS runs `ipconfig /registerdns`,
triggering DNS registration for all interfaces that do not explicitly disable it.
In this PR, we update dns/windowsManager.disableDynamicUpdates to also set RegistrationEnabled to 0.
Fixes#13411
Signed-off-by: Nick Khyl <nickk@tailscale.com>
4dfde7bffc