Updates tailscale/corp#20969
Right now, when netcheck starts, it asks tailscaled for a copy of the DERPMap. If it doesn't have one, it makes a HTTPS request to controlplane.tailscale.com to fetch one.
This will always fail if you're on a network with a captive portal actively blocking HTTPS traffic. The code appears to hang entirely because the http.Client doesn't have a Timeout set. It just sits there waiting until the request succeeds or fails.
This adds a timeout of 10 seconds, and logs more details about the status of the HTTPS request.
Signed-off-by: Andrea Gottardo <andrea@gottardo.me>
8eb15d3d2d