[MM] Report BufferingState based on the actual buffering status.
Report BufferingState based on actual espp buffering status.
If it can play when buffered timestamp is 500ms greater than current timestamp
then report BUFFERING_HAVE_ENOUGH.
If current timestamp is greater than buffered timestamp or buffer is flushed
then report BUFFERING_HAVE_NOTHING.
Reporting BufferingState affects setting WebMediaPlayer::ReadyState.
Change-Id: Ice1a8a42a576d62b8b1e837847e5853dcd5156de
Signed-off-by: Sun-woo Nam <sunny.nam@samsung.com>