NFS: Don't return layout segments that are in use

If the NFS_LAYOUT_RETURN_REQUESTED flag is set, we want to return the
layout as soon as possible, meaning that the affected layout segments
should be marked as invalid, and should no longer be in use for I/O.

Fixes: f0b42981 ("pNFS: Ignore non-recalled layouts in pnfs_layout_need_return()")
Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>