libavformat/mpegts: expose raw packet size

We cannot easily determine if an mpeg TS's packet size is DVHS, FEC
or so on, for that we need to expose the internal raw_packet_size
field.

Signed-off-by: Leandro Dorileo <leandro.maciel.dorileo@intel.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
