Changed to only allow SSL2 and SSL3 to be manually enabled.

See RFC 8996, Deprecating TLS 1.0 and TLS 1.1.
Also see NIST SP 800-52r2 which requires TLS 1.2 and TLS 1.3, should not use TLS 1.1, and shall not use TLS 1.0, SSL 3.0, or SSL 2.0.