send out of dialog BYE to node instead of rejecting

[tsearle]

[baonq-me]

Can you explain more about the PR ?

[davehorton]

I believe @tsearle had some scenario that involved him needing this change. However, I have not merged yet because I am not sure I agree with it....if we get a BYE that is not related to an established dialog, I still feel like the proper response is for the server to generate a 481 Transaction does not exist. Leaving this open for further discussion at the moment..

[tsearle]

The goal was to not use the dialog layer in drachtio, instead manage dialog state in the node app, that way it could be persisted & restored on restart for high availability reasons