There is a documentation error in the TSE User Guide saying that the frame is either transmitted to the GMII interface with an error or discarded by the MAC function when ff_tx_err is asserted.
In fact, the TSE MAC has transmitted the frame to GMII interface when ff_tx_err signal is asserted. There is no frame discard option in this condition.
The TSE User Guide is fixed on 8.0 release.