fix according RFC3261 12.1 Creation of a Dialog

[zusrut]

Fix for recent commit be7c0f4.
To send early BYE we must to have to-tag.

According RFC3261

12.1 Creation of a Dialog

Dialogs are created through the generation of non-failure responses
to requests with specific methods. Within this specification, only
2xx and 101-199 responses with a To tag, where the request was
INVITE, will establish a dialog.

[emiago]

We may need to-tag check to be this fully correct, but merging this as well.