NFS: Ensure NFSv4 SETCLIENTID send buffer is large enough

Ensure that the RPC buffer size specified for NFSv4 SETCLIENTID procedures
matches what we are encoding into the buffer.  See the definition of
struct nfs4_setclientid {} and the encode_setclientid() function.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>