In the receive direction, a frame is flagged as errored for the same reasons
as the non-segmented case. Each segment contains an ERR signal,
rx_axis_tkeep_user_N[3]. An error is signaled when the MRMAC asserts the ERR signal at the same time as the EOP and ENA signals.
In the event of a signaled error, the user logic is responsible for discarding the packet.