Refine special_small_blocks property validation

When the special_small_blocks property is being set during a pool
create it enforces a limit of 128KiB even if the pool's record size
is larger.

If the recordsize property is being set during a pool create, then
use that value instead of the default SPA_OLD_MAXBLOCKSIZE value.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Don Brady <dev.fs.zfs@gmail.com>
Closes #13815
Closes #14811