Rework map session

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>

integration/scenario.go

@@ -50,6 +50,8 @@ var (
 	tailscaleVersions2021 = map[string]bool{
 		"head":     true,
 		"unstable": true,
+		"1.60":     true,  // CapVer: 82
+		"1.58":     true,  // CapVer: 82
 		"1.56":     true,  // CapVer: 82
 		"1.54":     true,  // CapVer: 79
 		"1.52":     true,  // CapVer: 79