cmd/tailscaled: update ConfigureWebClient's UseSocketOnly value

Previously were always setting `UseSocketOnly` because we were
comparing `args.socketpath != ""`, but `args.socketpath` flag
always gets filled with `paths.DefaultTailscaledSocket()` when
not provided. Rather than comparing to the empty string, compare
to the default value to determine if `UseSocketOnly` should be
set.

Should fix issue with web client being unreachable for Mac App
Store variant of the mac build.

Updates #16054

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -556,7 +556,10 @@ func getLocalBackend(ctx context.Context, logf logger.Logf, logID logid.PublicID
 	if root := lb.TailscaleVarRoot(); root != "" {
 		dnsfallback.SetCachePath(filepath.Join(root, "derpmap.cached.json"), logf)
 	}
-	lb.ConfigureWebClient(&tailscale.LocalClient{Socket: args.socketpath, UseSocketOnly: args.socketpath != ""})
+	lb.ConfigureWebClient(&tailscale.LocalClient{
+		Socket:        args.socketpath,
+		UseSocketOnly: args.socketpath != paths.DefaultTailscaledSocket(),
+	})
 	configureTaildrop(logf, lb)
 	if err := ns.Start(lb); err != nil {
 		log.Fatalf("failed to start netstack: %v", err)