EX-7818 osc: don't do decomp. with compression disabled

EX-7818 osc: don't do decomp. with compression disabled

decompress_request likely has a significant performance
cost for checking if data is compressed, so we should not
call it when compression is disabled.

This is a stop-gap solution for the preview until we can
have the server tell the client if data is compressed, as
described in EX-7818.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Iba8feba3ab0fe620d0594f59c2c6ddea25faeb4f
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51563
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>