4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>

*** 2180,2190 ****
                          if (rc->rc_error == 0)
                                  continue;
  
                          zio_nowait(zio_vdev_child_io(zio, NULL, cvd,
                              rc->rc_offset, rc->rc_data, rc->rc_size,
!                             ZIO_TYPE_WRITE, zio->io_priority,
                              ZIO_FLAG_IO_REPAIR | (unexpected_errors ?
                              ZIO_FLAG_SELF_HEAL : 0), NULL, NULL));
                  }
          }
  }
--- 2180,2190 ----
                          if (rc->rc_error == 0)
                                  continue;
  
                          zio_nowait(zio_vdev_child_io(zio, NULL, cvd,
                              rc->rc_offset, rc->rc_data, rc->rc_size,
!                             ZIO_TYPE_WRITE, ZIO_PRIORITY_ASYNC_WRITE,
                              ZIO_FLAG_IO_REPAIR | (unexpected_errors ?
                              ZIO_FLAG_SELF_HEAL : 0), NULL, NULL));
                  }
          }
  }