NFSv4: Simplify the struct nfs4_stateid

Replace the union with the common struct stateid4 as defined in both
RFC3530 and RFC5661. This makes it easier to access the sequence id,
which will again make implementing support for parallel OPEN calls
easier.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index c190e9c..6f1c1e3 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -496,12 +496,12 @@
 {
 	u32 oldseq, newseq;
 
-	oldseq = be32_to_cpu(lo->plh_stateid.stateid.seqid);
-	newseq = be32_to_cpu(new->stateid.seqid);
+	oldseq = be32_to_cpu(lo->plh_stateid.seqid);
+	newseq = be32_to_cpu(new->seqid);
 	if ((int)(newseq - oldseq) > 0) {
 		nfs4_stateid_copy(&lo->plh_stateid, new);
 		if (update_barrier) {
-			u32 new_barrier = be32_to_cpu(new->stateid.seqid);
+			u32 new_barrier = be32_to_cpu(new->seqid);
 
 			if ((int)(new_barrier - lo->plh_barrier))
 				lo->plh_barrier = new_barrier;
@@ -525,7 +525,7 @@
 			int lget)
 {
 	if ((stateid) &&
-	    (int)(lo->plh_barrier - be32_to_cpu(stateid->stateid.seqid)) >= 0)
+	    (int)(lo->plh_barrier - be32_to_cpu(stateid->seqid)) >= 0)
 		return true;
 	return lo->plh_block_lgets ||
 		test_bit(NFS_LAYOUT_DESTROYED, &lo->plh_flags) ||
@@ -759,7 +759,7 @@
 		}
 	if (!found) {
 		struct pnfs_layout_hdr *lo = nfsi->layout;
-		u32 current_seqid = be32_to_cpu(lo->plh_stateid.stateid.seqid);
+		u32 current_seqid = be32_to_cpu(lo->plh_stateid.seqid);
 
 		/* Since close does not return a layout stateid for use as
 		 * a barrier, we choose the worst-case barrier.