livehttp: add DISCONTINUITY on playlist if we have restarted stream
livehttp: add DISCONTINUITY on playlist if we have restarted stream

If provided initial-segment-number option, signal discontinuity so
player knows to reset timestamps etc for new segments.

xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,krichter722/vlc,krichter722/vlc,xkfz007/vlc,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,vlc-mirror/vlc,vlc-mirror/vlc,shyamalschandra/vlc,vlc-mirror/vlc,krichter722/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,shyamalschandra/vlc,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,xkfz007/vlc,krichter722/vlc