ICE session should be kept alive even when media is marked as inactive

[bennylp]

In double hold situation, media will be marked as a=inactive. When the media is reactivated again (the call is resumed), it looks like we unnecessarily restart ICE negotiation, which will fail if remote still has the ICE session intact.

More over, isn't it that we should keep sending keep-alive packets and maybe even RTCP packets even when the media is marked as inactive? This would be the argument to keep ICE session alive when media is inactive.