sending.
When a peer leaves a group, they send a packet to the group
indicating that they're leaving. However if this packet is sent
via TCP, it gets put in a packet queue, which is then destroyed
on the rest of the group cleanup process before ever being able
to send.
This pr allows do_gc() to finish an iteration before cleaning the
group up, which allows the TCP packet queue to be emptied. However
this bug still exists on a tox_kill() event because we don't have
a chance to do another do_gc() iteration.
We now depend on libsodium unconditionally. Future work will require
functions from libsodium, and nobody we're aware of uses the nacl build
for anything other than making sure it still works on CI.
This function will return an IP address string associated with a peer.
If the peer is not accepting direct connections a placeholder value
will be returned, indicating that their real IP address is unknown.
We do not return TCP relay IP addresses because a TCP connection
with a peer may use multiple relays simultaneously.
