Offer an outgoing stream tube.
When the tube has been offered, callback will be called. You can then call offer_async.end to
get the result of the operation.
You have to connect to the incoming signal to get a StreamTubeConnection each time a contact establishes a connection to the tube.
| this |
an outgoing StreamTubeChannel |
| callback |
a callback to call when the tube has been offered |
| params |
parameters of the tube, or |
| user_data |
data to pass to |