btrfs: test read corruption of compressed extents differently

btrfs: test read corruption of compressed extents differently

Regression test for file read corruption when using compressed extents
that represent file ranges with a length that is a multiple of 16 pages
and that are shared by multiple consecutive ranges of the same file.

This is similar to the test added in commit 694db0c050d6 ("btrfs: read
corruption of compressed extents"), but tests the special case where the
extent's uncompressed length is a multiple of 16 pages. The first btrfs
fix, tested by the test added in the commit mentioned before, failed to
address this special case.

This btrfs issue is fixed by the linux kernel patch titled:
"Btrfs: update fix for read corruption of compressed and shared extents"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>