[Discussion] Add ENABLE_TLS option

[beef9999]

We already have the ENABLE_SASL option which is default OFF, and we used to regard that SSL module is a MUST HAVE.

But the SSL init in net/security-context/tls-stream.cpp will register Photon mutex, and will potentially cause core dumps if the app has used other third-party libs depends on SSL.

Since we can't remove all the third-party which might still be using std::threads, we sometimes need to disable SSL in Photon.

The new ENABLE_TLS option will only affect RPC client and HTTP client, and can defaults to ON.

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Another option is not to add this option, but to change RPC client API. If not passing a TLSContext*, the TLS stream will not be initialized, so the SSL global init will not be called.

[jiangdongzi]

IMO TLS is misleading. Developers may think it means thread local storage

[lihuiba]

IMO TLS is misleading. Developers may think it means thread local storage

Yes, I believe so. I once had such confusion. Is there any suggestions?