Fix DMA synchronization in the ENA driver Tx and Rx paths
The DMA in FreeBSD requires explicit synchronization. ENA driver was
only doing PREREAD and PREWRITE synchronizations. Missing
bus_dmamap_sync() calls were added.
It is also required to synchronize DMA engine before unloading DMA map.
Submitted by: Michal Krawczyk <firstname.lastname@example.org>
Obtained from: Semihalf
Sponsored by: Amazon, Inc.