disabled resilver_defer feature leads to looping resilvers

illumos/illumos-gate@233f6c49954dadfb21fa0809febd15e2160e0ff5
https://github.com/illumos/illumos-gate/commit/233f6c49954dadfb21fa0809febd15e2160e0ff5

Note: unusually for illumos this commit does not have a bug ID.

Author: Kody Kantor <kody@kkantor.com>