NFS: Micro-optimize nfs4_decode_dirent()

Make the decoding of NFSv4 directory entries slightly more efficient
by:

  1.  Avoiding unnecessary byte swapping when checking XDR booleans,
      and

  2.  Not bumping "p" when its value will be immediately replaced by
      xdr_inline_decode()

This commit makes nfs4_decode_dirent() consistent with similar logic
in the other two decode_dirent() functions.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4xdr.c

@@ -6086,11 +6086,11 @@ int nfs4_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	__be32 *p = xdr_inline_decode(xdr, 4);
 	if (unlikely(!p))
 		goto out_overflow;
-	if (!ntohl(*p++)) {
+	if (*p == xdr_zero) {
 		p = xdr_inline_decode(xdr, 4);
 		if (unlikely(!p))
 			goto out_overflow;
-		if (!ntohl(*p++))
+		if (*p == xdr_zero)
 			return -EAGAIN;
 		entry->eof = 1;
 		return -EBADCOOKIE;
@@ -6101,7 +6101,7 @@ int nfs4_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 		goto out_overflow;
 	entry->prev_cookie = entry->cookie;
 	p = xdr_decode_hyper(p, &entry->cookie);
-	entry->len = ntohl(*p++);
+	entry->len = be32_to_cpup(p);
 
 	p = xdr_inline_decode(xdr, entry->len);
 	if (unlikely(!p))