EX-7601 ofd: round read lock to chunk

EX-7601 ofd: round read lock to chunk

For unaligned reads, we need to round the read locking to
cover the any leading or trailing chunks.  We do this by
creating a local 'remote niobuf' to describe the rounded
range and doing the locking against that niobuf.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I8818522c188aca3c5c5eb564da2a8ba8aef18a4b
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52864
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>