Upstream: zdb inode mapping

Unfortunately macOS reserves inode ID numbers 0-15, and we can
not used them. In macOS port we simply map them really high IDs.

Normally this is hidden inside the _os implementation, but this is
the one place in the common source files.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Jorgen Lundman <lundman@lundman.net>
Closes #12530