refactor filer_pb.Entry and filer.Entry to use GetChunks()

for later locking on reading chunks

weed/filer/etcd/etcd_store.go

@@ -82,7 +82,7 @@ func (store *EtcdStore) InsertEntry(ctx context.Context, entry *filer.Entry) (er
 		return fmt.Errorf("encoding %s %+v: %v", entry.FullPath, entry.Attr, err)
 	}
 
-	if len(entry.Chunks) > filer.CountEntryChunksForGzip {
+	if len(entry.GetChunks()) > filer.CountEntryChunksForGzip {
 		meta = weed_util.MaybeGzipData(meta)
 	}