Added LC3PLUS_LEA_COMPAT_BITRATES_48_6 flag to treat split-rendering 256kbps...

Added LC3PLUS_LEA_COMPAT_BITRATES_48_6 flag to treat split-rendering 256kbps lc3plus 10ms 0dof bitrate as sentinel value for LEA compatible 48_6 bitrate (124 kbps per channel)