Continuing work in 434af15a04, to make it possible for magicsock to
probe whether a DERP server is still there.
Updates #3619
Change-Id: I366a77c27e93b876734e64f445b85ef01eb590f2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
It just has a version number in it and it's not really needed.
Instead just return it as a normal Recv message type for those
that care (currently only tests).
Updates #150 (in that it shares the same goal: initial DERP latency)
Updates #199 (in that it removes some DERP versioning)
The magicsock derpReader was holding onto 65KB for each DERP
connection forever, just in case.
Make the derp{,http}.Client be in charge of memory instead. It can
reuse its bufio.Reader buffer space.
This allows tailscaled's own traffic to bypass Tailscale-managed routes,
so that things like tailscale-provided default routes don't break
tailscaled itself.
Progress on #144.
Signed-off-by: David Anderson <danderson@tailscale.com>