SSL: fixed build with OPENSSL_NO_DEPRECATED defined.

The RSA_generate_key() is marked as deprecated and causes build to
fail.  On the other hand, replacement function, RSA_generate_key_ex(),
requires much more code.  Since RSA_generate_key() is only needed
for barely usable EXP ciphers, the #ifdef was added instead.

Prodded by Piotr Sikora.