control/controlclient: introduce eventbus messages instead of callbacks (#16956)

This is a small introduction of the eventbus into controlclient that
communicates with mainly ipnlocal. While ipnlocal is a complicated part
of the codebase, the subscribers here are from the perspective of
ipnlocal already called async.

Updates #15160

Signed-off-by: Claus Lensbøl <claus@tailscale.com>

control/controlclient/auto.go

@@ -205,7 +205,6 @@ func NewNoStart(opts Options) (_ *Auto, err error) {
 		}
 	})
 	return c, nil
-
 }
 
 // SetPaused controls whether HTTP activity should be paused.
@@ -424,6 +423,11 @@ func (c *Auto) unpausedChanLocked() <-chan bool {
 	return unpaused
 }
 
+// ClientID returns the ClientID of the direct controlClient
+func (c *Auto) ClientID() int64 {
+	return c.direct.ClientID()
+}
+
 // mapRoutineState is the state of Auto.mapRoutine while it's running.
 type mapRoutineState struct {
 	c  *Auto