NFSv4: Ensure that the NFSv4 locking can recover from stateid errors

In most cases, we just want to mark the lock_stateid sequence id as being
uninitialised.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>