AMR Rate Adaptation uses BER instead of C/I thresholds
For some non-obvious reason,
trx_loop_amr_input() uses the BER for switching AMR modes, rather than the C/I which is specified in 3GPP TS 45.009. This should be changed to use C/I and be spec compliant. Note that this only applioes to osmo-bts-trx. The other osmo-bts back-ends have the PHY/DSP handle this, and we assume those implementations are correct.
There also is no C/I normalization as per Annex A of the same specification.