NFSv4: Only increment the sequence id if the server saw it

It is quite possible that the OPEN, CLOSE, LOCK, LOCKU,... compounds fail
before the actual stateful operation has been executed (for instance in the
PUTFH call). There is no way to tell from the overall status result which
operations were executed from the COMPOUND.

The fix is to move incrementing of the sequence id into the XDR layer,
so that we do it as we process the results from the stateful operation.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>