parse: dont demux or count towards statistics unless the PID is selected

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
parse: dont invoke the demuxer unless DVBTEE_DEMUXER is defined at build-time

This feature is for debug, only. It is always on, so it should be left out of
the default build until the feature is made optional. For now, to enable it
just add "-DDVBTEE_DEMUXER" to CPPFLAGS in libdvbtee/Makefile

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>