* I2PTunnel bugfix (thanks Complication!)
* Increase the SSU cwin slower during congestion avoidance (at k/cwin^2
instead of k/cwin)
* Limit the number of inbound SSU sessions being built at once (using
half of the i2np.udp.maxConcurrentEstablish config prop)
* Don't shitlist on a message send failure alone (unless there aren't any
common transports).
* More careful bandwidth bursting