MFV r348596: 9689 zfs range lock code should not be zpl-specific
illumos/illumos-gate@7931524763ef94dc16989451dddd206563d03bb4
FreeBSD note: some tweaking was needed to avoid a conflict with
sys/rangelock.h.
Author: Matthew Ahrens <mahrens@delphix.com>
Obtained from: illumos
MFC after: 3 weeks