Added comment to check why that field is needed

src/main/java/net/schmizz/sshj/sftp/RemoteFile.java

@@ -88,6 +88,7 @@ public class RemoteFile
             throws IOException {
         return requester.request(newRequest(PacketType.WRITE)
                                          .putUInt64(fileOffset)
+                                        // TODO The SFTP spec claims this field is unneeded...? See #187
                                          .putUInt32(len)
                                          .putRawBytes(data, off, len)
         );