Implement control over command reordering via options and control mode page.

It allows to bypass range checks between UNMAP and READ/WRITE commands,
which may introduce additional delays while waiting for UNMAP parameters.
READ and WRITE commands are always processed in safe order since their
range checks are almost free.
Fix error handling in cpuset_setithread() introduced in r267716.

Noted by:	kib
MFC after:	1 week