ZTS: resilver_restart_001.ksh restore defaults

Update resilver_restart_001.ksh to restore the default
resilver_defer_percent when the test completes.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Pavel Snajdr <snajpa@snajpa.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #16618