OpenZFS 8984 - fix for 6764 breaks ACL inheritance

Authored by: Dominik Hassler <hadfl@omniosce.org>
Reviewed by: Sam Zaydel <szaydel@racktopsystems.com>
Reviewed by: Paul B. Henson <henson@acm.org>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Matthew Ahrens <mahrens@delphix.com>
Ported-by: Paul B. Henson <henson@acm.org>

OpenZFS-issue: https://www.illumos.org/issues/8984
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/e9bacc6d1a
Closes #10266