vp9-rtc: Allow simulcast mode for flexible/bypass mode
vp9-rtc: Allow simulcast mode for flexible/bypass mode

Change-Id: I0252d06c4f21d7c700c81d387bef89646229a63c

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