prepend @setDataFrame fix

In current versions of ffmpeg, when streaming to an RTMP server, anytime a packet of type `RTMP_PT_NOTIFY` is encountered, the packet is prepended with `@setDataFrame` before it gets sent to the server. This is incorrect; only packets for `onMetaData` and `|RtmpSampleAccess` should invoke `@setDataFrame` on the RTMP server. Specifically, the current bug manifests itself when trying to stream `onTextData` or `onCuePoint` invocations.

This fix addresses that problem and ensures that the `@setDataFrame` is only prepended for `onMetaData` and `|RtmpSampleAccess`.