cpu/stm32/periph_eth: fix error handling
cpu/stm32/periph_eth: fix error handling

An earlier version of periph_eth used to always pack the first chunk of the
outgoing frame to the first DMA descriptor by telling the DMA to jump back
to the first descriptor within the last descriptor. This worked fine unless
the frame was send in one chunk (as e.g. lwip does), which resulted due to a
hardware bug in a frame being send out twice. For that reason, the behavior was
changed to cycle throw the linked DMA descriptor list in round-robin fashion.
However, the error checking was not updated accordingly. Hence, the error
check might run over (parts of) unrelated frames and fail to detect errors
correctly.

This commit fixes the issue and also provides proper return codes for errors.

Additionally, an DMA reset is performed on detected errors during RX/TX. I'm
not sure if/when this is needed, as error conditions are neigh impossible to
produce. But better be safe than sorry.

ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,authmillenon/RIOT,OTAkeys/RIOT,jasonatran/RIOT,ant9000/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kYc0o/RIOT,miri64/RIOT,authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,kYc0o/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,authmillenon/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,jasonatran/RIOT,miri64/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,authmillenon/RIOT,miri64/RIOT,kYc0o/RIOT,jasonatran/RIOT,miri64/RIOT,kYc0o/RIOT,ant9000/RIOT,OlegHahm/RIOT,ant9000/RIOT