If an error is encountered while fetching a descriptor, the QDMA Descriptor
Engine flags the descriptor with error. For a queue in internal mode, the H2C Stream
Engine handles the error descriptor by not performing any PCIe or DMA activity. Instead,
it waits for the error descriptor to pass through the pipeline and forces a writeback
after it is done. For a queue in bypass mode, it is the responsibility of the user logic
to not issue a batch of descriptors with an error descriptor. Instead, it must send just
one descriptor with error input asserted on the H2C Stream bypass-in interface and set
the SOP, EOP, no_dma signal, and sdi or mrkr-req signal to make the H2C
Stream Engine send a writeback to Host.