filer: etcd fix pagination

fix https://github.com/chrislusf/seaweedfs/issues/3016

weed/filer/etcd/etcd_store.go

@@ -152,7 +152,7 @@ func (store *EtcdStore) ListDirectoryEntries(ctx context.Context, dirPath weed_u
 	}
 
 	resp, err := store.client.Get(ctx, string(lastFileStart),
-		clientv3.WithPrefix(), clientv3.WithSort(clientv3.SortByKey, clientv3.SortDescend))
+		clientv3.WithFromKey())
 	if err != nil {
 		return lastFileName, fmt.Errorf("list %s : %v", dirPath, err)
 	}