3747 txg commit callbacks don't work
Submitted by:   Will Andrews <willa@spectralogic.com>
Reviewed by:    Matthew Ahrens <mahrens@delphix.com>

*** 4511,4521 ****
           * commit callback hasn't been called, then most likely there's an
           * implementation bug..
           */
          tmp_cb = list_head(&zcl.zcl_callbacks);
          if (tmp_cb != NULL &&
!             tmp_cb->zcd_txg > txg - ZTEST_COMMIT_CALLBACK_THRESH) {
                  fatal(0, "Commit callback threshold exceeded, oldest txg: %"
                      PRIu64 ", open txg: %" PRIu64 "\n", tmp_cb->zcd_txg, txg);
          }
  
          /*
--- 4511,4521 ----
           * commit callback hasn't been called, then most likely there's an
           * implementation bug..
           */
          tmp_cb = list_head(&zcl.zcl_callbacks);
          if (tmp_cb != NULL &&
!             (txg - ZTEST_COMMIT_CALLBACK_THRESH) > tmp_cb->zcd_txg) {
                  fatal(0, "Commit callback threshold exceeded, oldest txg: %"
                      PRIu64 ", open txg: %" PRIu64 "\n", tmp_cb->zcd_txg, txg);
          }
  
          /*