ipn: call SetNetInfoCallback later, in Start

It was being called back into ultimately from magicsock before there
was a control client.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/local.go

@@ -87,8 +87,6 @@ func NewLocalBackend(logf logger.Logf, logid string, store StateStore, e wgengin
 	}
 	b.statusChanged = sync.NewCond(&b.statusLock)
 
-	e.SetNetInfoCallback(b.SetNetInfo)
-
 	if b.portpoll != nil {
 		go b.portpoll.Run(ctx)
 		go b.runPoller()
@@ -290,6 +288,8 @@ func (b *LocalBackend) Start(opts Options) error {
 		b.send(Notify{Engine: &es})
 	})
 
+	b.e.SetNetInfoCallback(b.SetNetInfo)
+
 	b.mu.Lock()
 	prefs := b.prefs.Clone()
 	b.mu.Unlock()