Illumos 6293 - ztest failure: error == 28 (0xc == 0x1c) in ztest_tx_assign()

Illumos 6293 - ztest failure: error == 28 (0xc == 0x1c) in ztest_tx_assign()

6293 ztest failure: error == 28 (0xc == 0x1c) in ztest_tx_assign()
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/issues/6293
  https://github.com/illumos/illumos-gate/commit/8fe00bf

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>