Regardless of the name, the removed trace doesn't contain meaningful
Hangout traffic.
Remove last piece of sub-classifiction based only on ip addresses.
The two fields `flow->flow_type` and `flow->protos.rtp.stream_type` are
pretty much identical: rename the former in `flow->flow_multimedia_type`
and remove the latter.
Try avoiding false positives: look for 3 RTP packets before classifing
the flow as such.
Add a generic function `is_rtp_or_rtcp()` to identify RTP/RTCP packets also
in other dissectors (see 3608ab01b commit message for an example)
