hlsenc.c, segment.c: propagate defaults to mpegts

This fixes the abnormally high ts overhead in the files produced by the
HLS and segments muxers. See https://trac.ffmpeg.org/ticket/2857 . For
example makes it much more likely that it can produces streams that fit
under the 64kb App store limit.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
