EX-7601 ofd: add read lnb to ofd_preprw_write

EX-7601 ofd: add read lnb to ofd_preprw_write

The read phase of read-modify-write for compressed files
needs to read only a subset of the pages which will be
written, so it needs a separate set of lnb pointers for
tracking this subset.

This patch passes around the necessary argument but does
not set up or use the lnb yet.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I7ec7101e65e73a6c9e67cea3c58d8cace38e70e0
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52984
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>