Fix: use stream's current tracefile count rather than the max

Fix: use stream's current tracefile count rather than the max

consumer_stream_create_output_files() formats the file name of a
stream's data file by passing the tracefile count setting rather than
using `tracefile_count_current`, the current "index" within the
on-disk ring buffer. This broke the trace file rotation functionality
as the same file would be overwritten continuously.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>