Keep the base directory of a relay session separate

For the session rotation feature, we need a way to modify the path of a
channel, so we need to keep the "<hostname>/<session-name>" information
separate in the consumer_net structure for future use.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>