5661 ZFS: "compression = on" should use lz4 if feature is enabled

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Reviewed by: Xin LI <delphij@freebsd.org>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Justin T. Gibbs <justing@spectralogic.com>

illumos/illumos-gate@db1741f555ec79def5e9846e6bfd132248514ff