Add --enable-openssl-method to socat build configuration

[ravomavain]

Socat has deprectated the use of the openssl-method option to choose which version of SSL/TLS to use. The intended replacement is openssl-min-proto-version and openssl-max-proto-version, but it's not available with openssl 1.0.2 (and probably don't support old ssl versions)

With this config flag, we can enable again the openssl-method option to choose which SSL / TLS version to use.

It's obviously deprecated/insecure (especially with old methods), just like openssl-pm-snapshot.