The ofconn_send_error in handle_flow_monitor_request uses the inner layer, which may cause heap overflow

[cotyleton]

The ofp header has been pulled at the ofputil_decode_flow_monitor_request, b->data points to the inner layer. As a result, if we need to send error reply, the ofconn_send_error would incorrectly processe the inner layer as the message header. An incorrect length would be used when memcpy request to reply.