It turns out these Linux ioctls are unfortunately
architecture-dependent, and not endian-dependent.
Fixup some warning messages while we're at it, too.
Fixes: 14fa0abdcc7b6513 ("rewrite Linux nodatacow use in pure Perl w/o system")
Link: https://public-inbox.org/meta/YfdYqLhDVQRQ9NGT@codewreck.org/
Noticed-by: Dominique Martinet <asmadeus@codewreck.org>