EX-7601 llite: restrict overwrites during preview

EX-7601 llite: restrict overwrites during preview

EX-7601 is an issue where when modifying a compressed file
we do not correctly read-up and re-write existing
compressed data.

To avoid this, we can only allow writes which are not
aligned to compression chunk size when they are not
overwriting existing data, ie, when they are extending the
file.

This returns EINVAL for all writes to compressed files
which are not either chunk aligned or extending the file.
This should prevent users from hitting the data corruption
issue but still allows some basic usage.  This is intended
just for the preview period.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I0eea01e2249866a074afd0d0642fe6dce9a49664
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51259
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>