provide a callback to intercept TLS messages being sent
As mentioned in: #826 (comment 213450784)
To send TLS messages in QUIC packets, we need a way to capture the TLS messages being sent. This can be implemented by providing a callback that intercepts messages from the TLS stack.
The API would looks something like:
/* content_type_t is currently private */ typedef int (*gnutls_record_write_callback_t)(gnutls_session_t, unsigned epoch, content_type_t, gnutls_datum_t *data); void gnutls_record_set_write_callback(gnutls_session_t, gnutls_record_write_callback_t);