Create helper TS API to return the file descriptor associated with a SSL connection

[shinrich]

I needed this to simplify writing a plugin that needed some access to the SSL object information. For a variety of reasons, I didn't want to pull in a SSL library to fetch this information directly from the SSL object I could have retrieved from TSVConnSslConnectionGet.

I also had created a wrapper API to return the SNI, but I see that someone has already contributed that via the TSVConnSslSniGet function.