* Add a high level comment.
* Move locals closer to point of use.
* Use fnv* routines rather than explicit verification of success.
* Factor out duplicated code by introducing isspacelimit to clarify
behavior.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org>
Closes#12967