SSL_CTX_set_client_hello_cb
void SSL_CTX_set_client_hello_cb(SSL_CTX *c, SSL_client_hello_cb_fn cb,
SSL_CTX_set_client_hello_cb(server_ctx, client_hello_ignore_cb, server2_ctx);
SSL_CTX_set_client_hello_cb(server_ctx, client_hello_reject_cb, server2_ctx);
SSL_CTX_set_client_hello_cb(server_ctx, client_hello_nov12_cb, server2_ctx);
SSL_CTX_set_client_hello_cb(ctx, client_hello_cb, NULL);
SSL_CTX_set_client_hello_cb(sctx, full_client_hello_callback, &testctr);