SSL_set_tlsext_max_fragment_length
int SSL_set_tlsext_max_fragment_length(SSL *ssl, uint8_t mode);
SSL_set_tlsext_max_fragment_length(clnt_ssl,
if (!TEST_true(SSL_set_tlsext_max_fragment_length(ssl, TLSEXT_max_fragment_length_DISABLED))
|| !TEST_false(SSL_set_tlsext_max_fragment_length(ssl, TLSEXT_max_fragment_length_512)))