vp8: Increase rate threshold for overshoot-drop
vp8: Increase rate threshold for overshoot-drop

Increase the rate threshold for the dropping when
overshoot is detected during encoding. This helps
to prevent some unneccessary drops for hard content.

Change-Id: I258bf33883d46347efd44e1e192cb25c444d05fe

ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx