Fix OpenSSL 3.0 API deprecations

Frediano Ziglio requested to merge fziglio/spice:openssl3_updates into master

This series supersedes !211 (closed). Second commit is supposed to be merged in first one (from @elmarco). It reduces the conditional code replacing new APIs. A partial test is added (DH parameter). Another test is being prepared (for RSA ticket, working but need a bit of tidying).

Edited by Frediano Ziglio

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