Import Illumos revision bb411a08b05466bfe0c7095b6373bbc1587e259a (Matthew Ahrens):

    4188 assertion failed in dmu_tx_hold_free(): dn_datablkshift != 0
    Reviewed by: George Wilson <george.wilson@delphix.com>
    Reviewed by: Christopher Siden <christopher.siden@delphix.com>
    Approved by: Garrett D'Amore <garrett@damore.org>

Ticket: #3575