Can't connect with TLS 1.2 because TLS1.0 is hardcoded in StartTLS() method

[RichardMcgough]

I am able to connect to an Openfire XMPP server configured to require TLS 1.0 but it doesn't work with TLS 1.2. I traced this down to the StartTLS() method which sets the protocol to SslProtocols.Tls which specifies TLS 1.0.

I changed it to TLS 1.2 and it works. It seems the JabberClient should expose the desired TLS protocol as a property that can be configured when the client is instantiated.