Change ownership of admin socket before dropping permissions (#1336)

This is to allow access to the socket by members of the group that
permissions are dropped to.

cmd/yggdrasil/main.go

@@ -293,7 +293,7 @@ func main() {
 
 	// Change user if requested
 	if *chuserto != "" {
-		err = chuser(*chuserto)
+		err = chuser(*chuserto, cfg.AdminListen)
 		if err != nil {
 			panic(err)
 		}