LU-16468 llite: protect layout before read IO going

LU-16468 llite: protect layout before read IO going

It's possible that the before the read IO, file_read_confine_iter()
->lov_attr_get() to get proper kms (known minimum size of the file),
and lov_attr_get() presumes that it's called under ongoing IO, which
protected the layout from changing, while it's not in this case.

Lustre-change: https://review.whamcloud.com/49622
Lustre-commit: from e050b91c6c471d3576eba3bbf4f3c31aef644e3f

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I1b36ec6e158331e63e8026ee2b986d5a7e3cb6dc
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49623
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>