ssp_ctx_next_token
err = ssp_ctx_next_token(ctx, NULL, &send_mb);
err = ssp_ctx_next_token(ctx, &recv_mb, &send_mb);
(void) ssp_ctx_next_token(ctx, &recv_mb, NULL);
int ssp_ctx_next_token(struct smb_ctx *, struct mbdata *, struct mbdata *);