EX-7601 osc: handle partial chunks in decompress_request

EX-7601 osc: handle partial chunks in decompress_request

Now that we have compression for incomplete chunks at the
end of files, decompress_request needs to handle these
chunks.  This patch modifies it to understand compressed
chunks which are less than chunk_size pages.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I877550fa0d418def406e0308392a5336ec9f3ab6
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53160
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>