ZFS send/recv with ashift 9->12 leads to data corruption

Improve the ability of zfs send to determine if a block is compressed
or not by using information contained in the blkptr.

Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Reviewed-by: Matthew Ahrens <matthew.ahrens@delphix.com>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #12770