NFSv4.1: Fix the CREATE_SESSION slot number accounting

NFSv4.1: Fix the CREATE_SESSION slot number accounting

commit b519d408ea32040b1c7e10b155a3ee9a36660947 upstream.

Ensure that we conform to the algorithm described in RFC5661, section
18.36.4 for when to bump the sequence id. In essence we do it for all
cases except when the RPC call timed out, or in case of the server returning
NFS4ERR_DELAY or NFS4ERR_STALE_CLIENTID.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
[bwh: Backported to 3.2:
 - Add the 'out' label
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>