Adobe Media Server and the like require that metadata is sent using
@setDataFrame. As such, in the relay module, when propagating metadata to
another server, we will use the @setDataFrame command.
It's possible that we'll receive NetStream.Publish.Start _before_ the codec
module has parsed the meta data. To handle that case, we'll also try to call
@setDataFrame when we receive the @setDataFrame from the publisher.