cmd/tailscale/cli: ensure custom UsageFunc is always set (#8665)

Updates #6995

Signed-off-by: Chris Palmer <cpalmer@tailscale.com>

cmd/tailscale/cli/cli.go

@@ -134,11 +134,6 @@ change in the future.
 		Exec:      func(context.Context, []string) error { return flag.ErrHelp },
 		UsageFunc: usageFunc,
 	}
-	for _, c := range rootCmd.Subcommands {
-		if c.UsageFunc == nil {
-			c.UsageFunc = usageFunc
-		}
-	}
 	if envknob.UseWIPCode() {
 		rootCmd.Subcommands = append(rootCmd.Subcommands,
 			idTokenCmd,
@@ -156,6 +151,12 @@ change in the future.
 		rootCmd.Subcommands = append(rootCmd.Subcommands, configureHostCmd)
 	}
 
+	for _, c := range rootCmd.Subcommands {
+		if c.UsageFunc == nil {
+			c.UsageFunc = usageFunc
+		}
+	}
+
 	if err := rootCmd.Parse(args); err != nil {
 		if errors.Is(err, flag.ErrHelp) {
 			return nil