Added function to create onion packets to send via TCP.
Decreased maximum onion_test test time.
If the path is a TCP one, the onion packet is sent with TCP.
Tox now closer to working on TCP only networks.

Use TCP paths when UDP is not connected.

Made some code depend less on the UDP only DHT.
Tox should now work on TCP only networks.

Coming soon: a function to disable UDP.