This commit restructures the map session in to a struct
holding the state of what is needed during its lifetime.
For streaming sessions, the event loop is structured a
bit differently not hammering the clients with updates
but rather batching them over a short, configurable time
which should significantly improve cpu usage, and potentially
flakyness.
The use of Patch updates has been dialed back a little as
it does not look like its a 100% ready for prime time. Nodes
are now updated with full changes, except for a few things
like online status.
Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>
