Parser: Allow connection line to be specified multiple times

[nemosupremo]

I've misplaced the wireshark output, but we ran into a situation where a camera's rtsp stream we were working with had specified the connection line multiple times; which caused sdp-types to fail parsing. This new just skips the duplicate lines instead. I can understand the rationale of failing on bad input, but I think the robustness principle applies.

[sdroege]

That makes sense, and I think we should do the same for all the other cases like this (no need to do this as part of this PR).

It would probably also make sense to add a dependency on the log crate and add a bit of logging, especially a warn! in these cases, as otherwise it might be surprising if information from the SDP simply disappears while parsing.

[sdroege]

The clippy warning should be gone now if you rebase

[sdroege]

@nemosupremo Any updates here?