At some point we started restarting map polls on health change, but we
don't remember why. Maybe it was a desperate workaround for something.
I'm not sure it ever worked.
Rather than have a haunted graveyard, remove it.
In its place, though, and somewhat as a safety backup, send those
updates over the HTTP/2 noise channel if we have one open. Then if
there was a reason that a map poll restart would help we could do it
server-side. But mostly we can gather error stats and show
machine-level health info for debugging.
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
fb4e23506f