Switch all bus_dmamap_sync calls that used PREREAD to PREWRITE and all POSTWRITE to POSTREAD.
Switch all bus_dmamap_sync calls that used PREREAD to PREWRITE and all
POSTWRITE to POSTREAD.

No guarantee that all busdma is usage is perfect, but this change (in
addition to scott's last two commits) makes if_bfe work with > 1GB of
memory in my laptop.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase