Unify set_arf_sign_bias function
Unify set_arf_sign_bias function

Determine if an ARF is on the future side by checking if its
offset meets the gop frame length. This unifies the support to
single- and multiple-layer ARF cases.

Change-Id: I5ab26f54311c345a9b574ffca5ff0a8dbcf4c031

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