The connstats package was an unnecessary layer of indirection.
It was seperated out of wgengine/netlog so that net/tstun and
wgengine/magicsock wouldn't need a depenedency on the concrete
implementation of network flow logging.
Instead, we simply register a callback for counting connections.
This PR does the bare minimum work to prepare tstun and magicsock
to only care about that callback.
A future PR will delete connstats and merge it into netlog.
Updates tailscale/corp#33352
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Joe Tsai