Fix to VP8 external RC for buffer levels
Fix to VP8 external RC for buffer levels

On a dynamic change of temporal layers:
starting/maimum/optimal were being set twice,
causing incorrect large values.

Bug: b/253927937
Change-Id: I204e885cff92530336a9ed9a4363c486c5bf80ae

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