V4L/DVB (7329): add flag to allow software demux to recognize the output type

Previously, the macro DVR_FEED, which is used to recognize and filter
out duplicate packets going to the DVR device, used the TS_PAYLOAD_ONLY
flag to identify a packet's destination.

This kind of filtering was introduced by the following two changesets:

Now, that it is possible to record TS PIDs using the demux device by
setting the output type to DMX_OUT_TSDEMUX_TAP, checking TS_PAYLOAD_ONLY
is not sufficient anymore. Therefore another flag, TS_DEMUX, is added to
specify the output type of a feed.

This allows multiple clients to filter the same TS PID on a demux device
simultaneously.

Signed-off-by: Andreas Oberritter <obi@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>