nfs: Don't increment lock sequence ID after NFS4ERR_MOVED

Xuan Qi reports that the Linux NFSv4 client failed to lock a file
that was migrated. The steps he observed on the wire:

1. The client sent a LOCK request to the source server
2. The source server replied NFS4ERR_MOVED
3. The client switched to the destination server
4. The client sent the same LOCK request to the destination
   server with a bumped lock sequence ID
5. The destination server rejected the LOCK request with
   NFS4ERR_BAD_SEQID

RFC 3530 section 8.1.5 provides a list of NFS errors which do not
bump a lock sequence ID.

However, RFC 3530 is now obsoleted by RFC 7530. In RFC 7530 section
9.1.7, this list has been updated by the addition of NFS4ERR_MOVED.
Reported-by: Xuan Qi <xuan.qi@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: stable@vger.kernel.org # v3.7+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

include/linux/nfs4.h

@@ -282,7 +282,7 @@ enum nfsstat4 {
 
 static inline bool seqid_mutating_err(u32 err)
 {
-	/* rfc 3530 section 8.1.5: */
+	/* See RFC 7530, section 9.1.7 */
 	switch (err) {
 	case NFS4ERR_STALE_CLIENTID:
 	case NFS4ERR_STALE_STATEID:
@@ -291,6 +291,7 @@ static inline bool seqid_mutating_err(u32 err)
 	case NFS4ERR_BADXDR:
 	case NFS4ERR_RESOURCE:
 	case NFS4ERR_NOFILEHANDLE:
+	case NFS4ERR_MOVED:
 		return false;
 	};
 	return true;