This rewrites the netlog package to support embedding node information in network flow logs.
Some bit of complexity comes in trying to pre-compute the expected size of the log message
after JSON serialization to ensure that we can respect maximum body limits in log uploading.
We also fix a bug in tstun, where we were recording the IP address after SNAT,
which was resulting in non-sensible connection flows being logged.
Updates tailscale/corp#33352
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
