This change adapts pion/ice to use a new interface for most network
related operations. The interface was formerly a simple struct vnet.Net
which was originally intended to facilicate testing. By replacing it
with an interface we have greater flexibility and allow users to hook
into the networking stack by providing their own implementation of
the interface.
PeerConnection used the public OnConnectionStateChange to track the
status of the ICETransport. This was incorrect because a user can
override this value at anytime.
Add a new internalOnConnectionStateChangeHandler that is set directly by
the PeerConnection and not accessible to the user.
In SetLocalDescription guard iceGatherer.Gather by checking state.
We don't put this check inside Gather because ORTC doesn't have the
function as re-entrant
Resolves#1144
Co-authored-by: jeremija
