[Galene] Redesigning the TURN functionality

[Juliusz Chroboczek <jch@irif.fr>]

On 18 July, Pascal wrote the following:

> Enabling TURN is the easiest way I found to manually provide this public
> IP address.  Maybe I could have patched the ICE gathering code instead.
> Or added STUN support.

Well, if you have access to a public STUN server, then you can simply
point Galene at the STUN server and be done.  Of course, unless the STUN
server also does TURN, you'll lose TURN functionality.

But what this discussion indicates is that the current built-in TURN
server works fine for globally-accessible servers, but doesn't work for
servers behind NAT.  So here's the plan:

1. rename -udp-range to -port-range, and have it control all of

  - the direct UDP port range;
  - the TURN UDP port range;
  - the TURN TCP port ragne.

2. add -udp-mux, which takes a single port, and only controls the direct
   UDP port being used.

It's a little bit more complicated, but more explicit.  Suggestions?

-- Juliusz