Pool allocation classes misplacing small file blocks
Due to an off-by-one condition in spa_preferred_class() we are picking
the "normal" allocation class instead of the "special" one for file
blocks with size equal to the special_small_blocks property value.
This change fix the small code issue, update the ZFS Test Suite and the
zfs(8) man page.
Reviewed-by: Brian Behlendorf <firstname.lastname@example.org>
Reviewed-by: Don Brady <email@example.com>
Signed-off-by: loli10K <firstname.lastname@example.org>