Changes are:
- Use the wrapper functions to access opaque data types. To preserve
backward compatibility, define fallback definitions
- Remove the use of idiom "pqueue_size(ssl->d1->sent_messages)", since
there is no replacement
- Use RSA_generate_key_ex instead of the deprecated RSA_generate_key
https://bugzilla.gnome.org/show_bug.cgi?id=773540
GST_DTLS_USE_GST_LOG is not defined anywhere, so
we'd just log into the default category by accident.
We use the gst logging system unconditionally now,
so might just as well remove this #if #else.