Revert "Linux 6.5 compat: register_sysctl_table removed"

This reverts commit b35374fd6474603170fd9a3c7503da6eb13ac712 as there
are error messages when loading the SPL module. Errors seemed to be tied
to duplicate a duplicate entry.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes #15134