LU-15963 osd-zfs: use contiguous chunk to grow blocksize

LU-15963 osd-zfs: use contiguous chunk to grow blocksize

otherwise a sparse OST_WRITE can grow blocksize way too large.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I729775490f9a0c8262708931f321297af943f3c0
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/47768
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>