Fix test_many_clients in tox_test

Stack variable to_comp goes out of scope,
but a reference to the variable is used later
in Fiend_Requests.
Spreading packets around TCP relays causes issues with the audio and video.

Make each connection stick to the same relay.
Size parameter is now checked in toxav_send_audio().

Cleaned up code a bit.
Merge branch 'master' of https://github.com/pyruvate/toxcore