Rate control fix for ARNR filtered frames.

Previously we had assumed that it was necessary to give a full frame's
bit allocation to the alt ref frame if it has been created through temporal
filtering. This is not the case. The active max quantizer control
insures that sufficient bits are allocated if needed and allocating a
full frame's worth of bits creates an excessive overhead for the ARF.

Change-Id: I83c95ed7bc7ce0e53ccae6ff32db5a97f145937a