nfs41: xdr {encode,decode}_sequence

Implement stubs for encode and decode sequence, defined as no-ops when
CONFIG_NFS_V4_1 is not defined.
Add the nfsv41 encode and decode sizes. Add encode_sequence to all
nfs4_enc_* routines and decode_sequence to all nfs4_dec_* routines as required
by v41.

[was nfs41: minorversion support for xdr]
[added nfs_client argument to encode_sequence so not to use sequence_args to pass sa_session]
Signed-off-by: Andy Adamson<andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[nfs41: pass *session in seq_args and seq_res]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>