EX-7601 ofd: multiple reads in same chunk

EX-7601 ofd: multiple reads in same chunk

When doing DIO or if we get unusual cache behavior on the
client, multiple reads can hit the same chunk.

This only shows up in racing tests, but it's important to
handle.  We do this by making sure we start searching the
lnbs for decompression at the start of the last chunk we
decompressed.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I81fbbba79b16066e6d4519c66030cc58e03d2de7
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53419
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>