implement interpacket gap for ethernet transmission.
fix reading of ethernet registers.
try to fix missing byte in video packet headers
turn video stream on by default.
change bit to control video capture.
fix bug with end of frame marker.
remove dummy byte after confirming problem is insertion, not deletion.
rejig frame announcement when streaming video.  now each raster line
is followed by a single 0x80 byte which effectively marks rasters and
frames.