OpenZFS 8418 - zfs_prop_get_table() call in zfs_validate_name() is a no-op

OpenZFS 8418 - zfs_prop_get_table() call in zfs_validate_name() is a no-op

Authored by: Marcel Telka <marcel@telka.sk>
Reviewed by: Vitaliy Gusev <gusev.vitaliy@icloud.com>
Approved by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>
OpenZFS-issue: https://www.illumos.org/issues/8418
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/e09ba01
Closes #6305