- adjust txhiwat and mindma params a bit
- fixed a couple of incorrectly labeled panic calls
- the "location" was being calculated incorrectly in some cases (forgot
to subtract off MID_RAMBASE). this only caused problem when trying
to change the size of the tx/rx buffers (e.g. to 64KB).
- fixed possible non-aligned DMA burst in the starting byte burst case.
(e.g. if we could DMA 3 bytes, but only have 2 it is not legal
for us to use MIDDMA_BYTE2 mode).
- opt: on tx: try and avoid flushing the internal buffer by padding out the
length of the last mbuf a bit (if possible)