Implement SSL_CTX_get_tlsext_status_cb

[Sp1l]

Allow access to tlsext_status_cb
This is a feature used in haproxy. Current patch (by me?) is also in OpenBSD ports and does not do what you'd want it to do...

[4a6f656c]

We will likely do this, however it is kinda crazy that an application would set a callback and then forget that it set a callback and needs to retrieve it via an API...

Also, that patch is actually dangerous - non-existent control values should not just be defined since there is a reason why the control value is missing. While we typically reuse the same control values as OpenSSL, there is no guarantee that we will, so a completely different control could be triggered instead of the one that is intended (and unimplemented).

[kinichiro]

6bb4328 fixed this issue.

[kinichiro]

@Sp1l Can you close this issue ?

[busterb]

I think we can just close it. Thanks.