We recently agreed that we will be sending an empty packet before
opening video streams in order to make sure that uni-directional streams
can reach destinations behind NATs.
I am now thinking that we could optimize this a little bit by only
sending the empty packets for recvonly streams (no point in doing it for
the other possible directions).
I am thinking we should probably also push this whole thing a bit deeper
in media, although having it in SIP also makes sense since that's where
all the ICE stuff will be and it's along the same lines. We should at
least move it to a separate method though, even if it stays in