sctp_error_auth_invalid_hmac
struct sctp_error_auth_invalid_hmac *cause;
op_err = sctp_get_mbuf_for_msg(sizeof(struct sctp_error_auth_invalid_hmac),
cause = mtod(op_err, struct sctp_error_auth_invalid_hmac *);
cause->cause.length = htons(sizeof(struct sctp_error_auth_invalid_hmac));
SCTP_BUF_LEN(op_err) = sizeof(struct sctp_error_auth_invalid_hmac);