The most serious bit of the substream_info header field (in a mayor sync
packet) indicates whether a 16-channel presentation is present in the
bitstream. If set, the extended_substream_info header field contains
information about the 16-channel presentation. This presentation always
uses substream 3, a substream that is discarded by truehd_core. So
substream_info needs to be changed to no longer indicate the presence
of a 16-channel presentation in order for truehd_core's output to be
consistent. This is implemented in this commit.

This change also makes MediaInfo no longer display the presence of Atmos
in the output of truehd_core.

Also, set the (now irrelevant) extended_substream_info field to zero as
this seems to be the common value for ordinary TrueHD.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>