Fix rtcpTransport description

[mparis]

This PR depends on #594

[alvestrand]

When you make two PRs that build on top of each other like this, please make a note of that in the description. It's otherwise confusing to see unrelated changes in the diff.

[aboba]

The PR removes statements describing the effect of BUNDLE which were put in to respond to another issue.

[alvestrand]

This seems to be the text Bernard's noting: "and will all send and receive RTCP over the same transport."

Needs a rebase now that its parent is merged.

[alvestrand]

Don't see the point here - it's not just a langauge cleanup, but it's not clear what it improves.
Unless a better reason is found, we'll close this.

[mparis]

With this patch, I want to clarify that the management of the rtcpTransport is the same in the case of BUNDLE that for rtcp-mux (it will be null), because BUNDLE mandates the usage of rtcp-mux.

[alvestrand]

It loses the explicit note that with BUNDLE, all the RTCP for all the flows will go over the same transport channel.
(I think that's what @aboba intended to say).

[alvestrand]

@mparis this is waiting for your response.

[aboba]

Replaced by rebased PR #677