ipn: apply tailnet-wide default for auto-updates (#10508)

When auto-update setting in local Prefs is unset, apply the tailnet
default value from control. This only happens once, when we apply the
default (or when the user manually overrides it), tailnet default no
longer affects the node.

Updates #16244

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

types/netmap/nodemut.go

@@ -176,5 +176,6 @@ func mapResponseContainsNonPatchFields(res *tailcfg.MapResponse) bool {
 		// PeersChanged to PeersChangedPatch in patchifyPeersChanged before this
 		// function is called, so it should never be set anyway. But for
 		// completedness, and for tests, check it too:
-		res.PeersChanged != nil
+		res.PeersChanged != nil ||
+		res.DefaultAutoUpdate != ""
 }

types/netmap/nodemut_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
+	"tailscale.com/types/opt"
 	"tailscale.com/types/ptr"
 )
 
@@ -26,6 +27,9 @@ func TestMapResponseContainsNonPatchFields(t *testing.T) {
 		case reflect.Bool:
 			return reflect.ValueOf(true)
 		case reflect.String:
+			if reflect.TypeOf(opt.Bool("")) == t {
+				return reflect.ValueOf("true").Convert(t)
+			}
 			return reflect.ValueOf("foo").Convert(t)
 		case reflect.Int64:
 			return reflect.ValueOf(int64(1))