control/controlclient: de-pointer Status.PersistView, document more

Updates #cleanup
Updates #1909

Change-Id: I31d91e120e3b299508de2136021eab3b34131a44
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -893,7 +893,6 @@ func (b *LocalBackend) SetDecompressor(fn func() (controlclient.Decompressor, er
 func (b *LocalBackend) SetControlClientStatus(st controlclient.Status) {
 	// The following do not depend on any data for which we need to lock b.
 	if st.Err != nil {
-		// TODO(crawshaw): display in the UI.
 		if errors.Is(st.Err, io.EOF) {
 			b.logf("[v1] Received error: EOF")
 			return
@@ -1007,8 +1006,8 @@ func (b *LocalBackend) SetControlClientStatus(st controlclient.Status) {
 		prefs.ControlURL = prefs.ControlURLOrDefault()
 		prefsChanged = true
 	}
-	if st.Persist != nil && st.Persist.Valid() {
-		if !prefs.Persist.View().Equals(*st.Persist) {
+	if st.Persist.Valid() {
+		if !prefs.Persist.View().Equals(st.Persist) {
 			prefsChanged = true
 			prefs.Persist = st.Persist.AsStruct()
 		}

ipn/ipnlocal/state_test.go

@@ -162,11 +162,10 @@ func (cc *mockControl) send(err error, url string, loginFinished bool, nm *netma
 		cc.mu.Unlock()
 	}
 	if cc.opts.Observer != nil {
-		pv := cc.persist.View()
 		s := controlclient.Status{
 			URL:     url,
 			NetMap:  nm,
-			Persist: &pv,
+			Persist: cc.persist.View(),
 			Err:     err,
 		}
 		if loginFinished {