zfs_ioc_snapshot: check user-prop permissions on snapshotted datasets
Previously, the permissions were checked on the pool which was obviously
incorrect.
After this change, zfs_check_userprops() only validates the properties
without any permission checks. The permissions are checked individually
for each snapshotted dataset.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Matt Ahrens <mahrens@delphix.com> Signed-off-by: Andriy Gapon <avg@FreeBSD.org>
Closes #9179
Closes #9180