- Ensure code which only applies to the control endpoint is not run
for other endpoints in the data transfer path.
- Ensure all bits of the "EPCON" register is written during
initialisation.

MFC after:	3 days
Reimplement WRITE USING TOKEN with Block Zero token using WRITE SAME.

On my ZVOL of SSDs that increases speed of zero writing in that way from
1 to 2.5GB/s by reducing CPU overhead.
MFC after:	2 weeks