When switching profile, the server URL can change (e.g.
because of switching to a self-hosted headscale instance).
If it is not reset here, dial plans returned by old
server (e.g. tailscale control server) will be used to
connect to new server (e.g. self-hosted headscale server),
and the register request will be blocked by it until
timeout, leading to very slow profile switches.
Updates #11938 11938
Signed-off-by: Shaw Drastin <showier.drastic0a@icloud.com>
