Add ice trickle support

[trivigy]

resolves pion/ice#51

[codecov-io]

Codecov Report

Merging #691 into master will decrease coverage by 0.23%.
The diff coverage is 64.4%.

@@            Coverage Diff             @@
##           master     #691      +/-   ##
==========================================
- Coverage   77.33%   77.09%   -0.24%     
==========================================
  Files          57       57              
  Lines        3644     3694      +50     
==========================================
+ Hits         2818     2848      +30     
- Misses        585      599      +14     
- Partials      241      247       +6

Impacted Files	Coverage Δ
icetransport.go	77.16% <0%> (-0.18%)	⬇️
peerconnection.go	70.88% <60%> (-0.98%)	⬇️
icegatherer.go	78.57% <69.35%> (-3.48%)	⬇️
dtlstransport.go	70.74% <0%> (+1.36%)	⬆️
sctptransport.go	72.72% <0%> (+1.39%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5e6149d...0ae5654. Read the comment docs.

[Sean-Der]

@trivigy Ok ready for a first pass!

It toggles between trickle/non-trickle if you have the callback set. When we do /v3 eventually we can break that behavior (and only do trickle)

I moved most of the behavior into ICEGatherer and had things follow ORTC stuff.

Can you try listening to OnICECandidate and then first time you get a srflx candidate try pulling pc.PendingLocalDescription

[trivigy]

One other thing if you don't mind addressing. There is inconsistency regarding what SessionDescription. Previously session description was extracted from CreateOffer() where it was returned as a struct instance. Now with trickle changes we need to extract it from LocalDescription() where it is returned as a pointer. This makes things inconsistent.

[Sean-Der]

One other thing if you don't mind addressing. There is inconsistency regarding what SessionDescription. Previously session description was extracted from CreateOffer() where it was returned as a struct instance. Now with trickle changes we need to extract it from LocalDescription() where it is returned as a pointer. This makes things inconsistent.

we need a way to express null, we can update this to return an error (but having no currentLocalDescription I don't believe is an error) so not sure what the answer is.