To streamcopy_init().
This will allow to simplify the control flow in ost_add() by moving the
ost_get_filters() call (which previously had to handle both encoding and
streamcopy streams) to ost_bind_filter() (which is only called for
audio/video encoding).
Also, return EINVAL rather than ENOSYS, as trying to combine filtering
with streamcopy is a parameter error.
71916aa107