OpenZFS 8520 - lzc_rollback

OpenZFS 8520 - lzc_rollback

8520 lzc_rollback_to should support rolling back to origin
7198 libzfs should gracefully handle EINVAL from lzc_rollback

lzc_rollback_to() should support rolling back to a clone's origin.
The current checks in zfs_ioc_rollback() would not allow that
because the origin snapshot belongs to a different filesystem.
The overly restrictive check was in introduced in 7600, but it
was not a regression as none of the existing tools provided a
way to rollback to the origin.

Authored by: Andriy Gapon <avg@FreeBSD.org>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@joyent.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
OpenZFS-issue: https://www.illumos.org/issues/8520
OpenZFS-issue: https://www.illumos.org/issues/7198
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/78a5a1a25a
Closes #7150