Use gst_util_dump_mem for packet content debug dump.
Use gst_util_dump_mem for packet content debug dump.

.. as we now depend on gstreamer library anyway.
It's a nice one function call instead of custom for loop, and outputs
it nicer as well (offset from start reported in addition to the
pointer value, and a string representation in the end, just like
in hexdump -C).

leio/libdvbsub,leio/libdvbsub