Draft: net: Bubble up HTTP error code in session_send_cb()
session_send_cb is the GAsyncReadyCallback for different call sites:
- get_file_async()
- put_file_async()
- queue_data()
Ensure that we consistently set the SoupMessage as data to the task which ends up calling session_send_cb() on completion to ensure we can grab the message and check it's status code.
Closes: #30