NFSv4.1: Get rid of the NFS_LAYOUT_DESTROYED state

We already have a mechanism for blocking LAYOUTGET by means of the
plh_block_lgets counter. The only "service" that NFS_LAYOUT_DESTROYED
provides at this point is to block layoutget once the layout segment
list is empty, which basically means that you have to wait until
the pnfs_layout_hdr is destroyed before you can do pNFS on that file
again.

This patch enables the reuse of the pnfs_layout_hdr if the layout
segment list is empty.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4filelayout.c b/fs/nfs/nfs4filelayout.c
index 6cce57e..52d8472 100644
--- a/fs/nfs/nfs4filelayout.c
+++ b/fs/nfs/nfs4filelayout.c
@@ -279,8 +279,7 @@
 {
 	struct nfs4_deviceid_node *node = FILELAYOUT_DEVID_NODE(lseg);
 
-	return pnfs_test_layout_destroyed(lseg->pls_layout) ||
-		filelayout_test_devid_unavailable(node);
+	return filelayout_test_devid_unavailable(node);
 }
 
 /*