Revert "Do not hold spa_config in ZIL while blocked on IO"

This reverts commit 7d638df09be7482935bcf6ec8e4ea2ac8a8be1a8.

Reviewed-by: Prakash Surya <prakash.surya@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Wilson <gwilson@delphix.com>
Closes #14678