NFSD: filecache: add STATX_DIOALIGN and STATX_DIO_READ_ALIGN support

NFSD: filecache: add STATX_DIOALIGN and STATX_DIO_READ_ALIGN support

Use STATX_DIOALIGN and STATX_DIO_READ_ALIGN to get DIO alignment
attributes from the underlying filesystem and store them in the
associated nfsd_file. This is done when the nfsd_file is first
opened for each regular file.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>