We still include them directly in the controlclient network map
just where we have been. Client plumbing we can do later.
Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
* adds new packet "netcheck" to do the checking of UDP, IPv6, and
nearest DERP server, and the Report type for all that (and more
in the future, probably pulling in danderson's natprobe)
* new tailcfg.NetInfo type
* cmd/tailscale netcheck subcommand (tentative name, likely to
change/move) to print out the netcheck.Report.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
