rtmp2src: support lower latency similar to ffmpeg's nobuffer option
When comparing ffplay -fflags nobuffer rtmp://xx.yy/zz/ww
with following pipeline:
gst-launch-1.0 rtmpsrc location=rtmp://xx.yy/zz/ww ! flvdemux ! decodebin ! autovideosink
There is about +7 seconds difference, which is a lot, and there is no exposed parameter to bring the latency down significantly.