BWE artefacts in HQ->ACELP transition

(Generic issue template)

The following code lines in acelp_core_enc.c and acelp_core_dec.c seems to cause problems for DFT stereo at 32 kbps which is running 16 kHz core. Likely, this approximation only works for 12.8 kHz core and needs to be adapted for 16 kHz core.

            if ( st->last_core != ACELP_CORE && st->element_mode > EVS_MONO )
            {
                /* Prepare ACB memory of old_bwe_exc */
                lerp( old_exc, old_bwe_exc, L_EXC_MEM_DEC * HIBND_ACB_L_FAC, L_EXC_MEM_DEC );
                
            }