Use the callbacks from the SSL object instead of the SSL_CTX object

... in functions dealing with the SSL object rather than the context.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2870)

(cherry picked from commit d61461a7)