vp9: Adjust some thresholds for noise estimation.
vp9: Adjust some thresholds for noise estimation.

Adjust thresholds for noise estimation, for resolutions above VGA.
Tends to push cleaner/low noise clips to LowLow state.

No change in RTC metrics.

Change-Id: I739ca6b797d0a60ccd1c6c6a2775269b1f007e5e

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