Rename certain functions for more consistency when they share common
features. Make comments clearer about what arguments should be passed
to the insert and add functions.
Reviewed by: Sara Hartse <sara.hartse@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes#9441
516a83f886