MFC r271360: Remove uninitialized and unused variable, reported by Coverity.
MFC r271313: Oops, missed piece of r271311.
MFC r271443: Add support for Extended INQUIRY Data (0x86) VPD page.
MFC r271503: Implement range checks between UNMAP and READ/WRITE commands.

Before this change UNMAP completely blocked other I/Os while running.
Now it blocks only colliding ones, slowing down others only due to ZFS
locks collisions.

Sponsored by:	iXsystems, Inc.