BUILD: ssl: replace SSL_CTX_get0_privatekey for openssl < 1.0.2

Commit 48a8332a introduce SSL_CTX_get0_privatekey in openssl-compat.h but
SSL_CTX_get0_privatekey access internal structure and can't be a candidate
to openssl-compat.h. The workaround with openssl < 1.0.2 is to use SSL_new
then SSL_get_privatekey.
2 files changed