Added minimal hooks in folly's AsyncSSLSocket API to allow an application to setup kTLS path

[Anirudha Pratap Singh]

kTLS is a way to offload ssl encrypt/decrypt etc. crypto operations to the kernel's TLS module.

The application which is invoking AsyncSSLSocket API will setup the kTLS path by doing appropriate setsockopt() calls and will subsequently set ktlsEnabled_ flag.

This will invoke send() system call instead of SSL_write to write the data. This makes all the data to go through kTLS module and hence gets offloaded to it.

The following pull request (feature request) contains the changes: https://github.com/facebook/folly/pull/1376

Please review the above PR.

Thanks,

-Anirudha