Remove database from Mapper

This commit changes the internals of the mapper to
track all the changes to peers over its lifetime.

This means that it no longer depends on the database
and this should hopefully help with locks and timing issues.
When the mapper is created, it needs the current list of peers,
the world view, when the polling session was started. Then as
update changes are called, it tracks the changes and generates
responses based on its internal list.

As a side, the types.Machines and types.MachinesP, as well as
types.Machine being passed as a full struct and pointer has been
changed to always be pointers, everywhere.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/mapper/tail.go

@@ -41,7 +41,7 @@ func tailNodes(
 // tailNode converts a Machine into a Tailscale Node. includeRoutes is false for shared nodes
 // as per the expected behaviour in the official SaaS.
 func tailNode(
-	machine types.Machine,
+	machine *types.Machine,
 	pol *policy.ACLPolicy,
 	dnsConfig *tailcfg.DNSConfig,
 	baseDomain string,