rtph264pay: Change aggregate-mode default for RTSP at least
See !2 (comment 527142) for details.
aggregate-mode=zero-latency is breaking various proprietary NVRs while they worked in previous versions and with
aggregate-mode=none. On the other hand Safari WebRTC doesn't work with no aggregation, which is why it was changed at all.
@ndufresne also says that
aggregate-mode=none behaviour now matches live555.