This adds an option to set the service type in mpegts as defined in ETSI 300 468.

I added what I believe are the most useful service types as pre defined values,
the others can be sent by using their hexdecimal form directly (e.g. -mpegts_service_type digital_radio, -mpegts_service_type 0x07).

I've been using this patch in order to pipe internet radio stream (originally as HLS/m3u8) from ffmpeg to tvheadend,
when the service type set right tvheadend recognize the mpegts stream as a radio channel.

The patch in its original form was written by linuxstb from freenode's hts channel which allowed me pushing it upstream.

This close issue 4118.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>