Way to call set_mode

[daurnimator]

To copy nginx' default SSL context setup, you need to be able to call:

SSL_CTX_set_mode(ssl->ctx, SSL_MODE_RELEASE_BUFFERS);
SSL_CTX_set_mode(ssl->ctx, SSL_MODE_NO_AUTO_CHAIN);

Cqueues also uses set_mode internally.

SSL_set_mode(ssl, SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);
SSL_set_mode(ssl, SSL_MODE_ENABLE_PARTIAL_WRITE);