Don't reset session on change_type

[axelson]

From looking at the code (and experimenting) it appears that when you have a change_type in your configuration, a new session is generated (unless there is one to restore from):

tsung/src/tsung/ts_client.erl

Line 488 in 4094df6

{_,_} -> % nothing to restore, or no restore asked, set new session

Instead I'd like to be able to keep the session that was previously being used. My use-case is that I am trying to do load testing of Phoenix LiveView and I need to keep the session from an HTTP request to a Websocket request. Is it possible to add such a configuration option?