Allow MediaStreamTrack.t() as a parameter to send_rtp/3

[srcrip]

hey, in my experimentation, this handle_cast for :send_rtp always receives a full track, not an id. This change makes everything work, but if you want it to be different feel free to edit my pr.

[srcrip]

Actually now that I'm looking at my code closer I realized it was in fact my fault. I was sending the track explicitly.

Since that's an easy mistake to make, would it be ok if I edit this function to accept a track or track id and just handle both appropriately?

[srcrip]

ok I've switched things up a bit:

• added a @doc for send_rtp
• made it able to accept track_id or mediastreamtrack, that way someone can mess up the way I did and it will just work

[LVala]

Thanks for the PR! SGTM, although the non-W3C functions in the API are quite experimental and may change in future versions, so this change might not be ever released, just keep that in mind.

We'll probably get back to it and merge on Monday.