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.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271507 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f