NFSv4.1: Get rid of pNFS layout state "NFS_LAYOUT_INVALID"

In all cases where we set NFS_LAYOUT_INVALID, we also set NFS_LAYOUT_DESTROYED.
Furthermore, in all cases where we test for NFS_LAYOUT_INVALID, we should
also be testing for NFS_LAYOUT_DESTROYED, since the latter means that
we hold no valid layout segments.
Ergo the two are redundant.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4filelayout.c b/fs/nfs/nfs4filelayout.c
index dac2162..6cce57e 100644
--- a/fs/nfs/nfs4filelayout.c
+++ b/fs/nfs/nfs4filelayout.c
@@ -190,8 +190,6 @@
 		 * i/o and all i/o waiting on the slot table to the MDS until
 		 * layout is destroyed and a new valid layout is obtained.
 		 */
-		set_bit(NFS_LAYOUT_INVALID,
-				&NFS_I(inode)->layout->plh_flags);
 		pnfs_destroy_layout(NFS_I(inode));
 		rpc_wake_up(&tbl->slot_tbl_waitq);
 		goto reset;
@@ -281,7 +279,7 @@
 {
 	struct nfs4_deviceid_node *node = FILELAYOUT_DEVID_NODE(lseg);
 
-	return filelayout_test_layout_invalid(lseg->pls_layout) ||
+	return pnfs_test_layout_destroyed(lseg->pls_layout) ||
 		filelayout_test_devid_unavailable(node);
 }