mTLS connection is not working

[zenonhun]

The currently implemented TLSSocket handling is not working with mTLS.
Even if the ca, key, pem files are set in the protocolOptions, the connection throws invalid certificate errors.

I did a manual test with the TLSSocket:

let opts = { port, host, ca, key, pem };

let socket = new TLSSocket();
socket.connect(opts);
// throws invalid certificate error. The client certificate is not sent properly.

socket=new TLSSocket(new Socket(opts), opts);
socket.connect(opts);
// no exception, however the socket stuck in 'opening' state

socket = tls.connect(opts)
// this time the connection is successfully opened

Seems like there are a lots of logic in tls.connect, beside creating a TLSSocket:
https://github.com/nodejs/node/blob/43f599b534e60933e86db4d9ad87dfd8750a0f06/lib/_tls_wrap.js#L1590

So probably to make winston-syslog work with TLS, the tls.connect() approach would be better.