Pushing the buffer via gst_pad_push () in transform_ip () function
causes downstream elements to process the buffer with a reference
count > 1. This leads to performance issue if there are downstream
elements which modify the buffer memory.
However, in drop-only mode this reference is not required.
So, let GstBaseTransform push the buffer in drop-only mode.
Fixes#4258
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9532>
e94830c79d