bsc: add TC_assignment_codec_amr_startmode_cruft

Make sure that when a 'start-mode auto' is set, that the previous start
mode setting does not linger in the unused bits.

- after I577ff590d7588fd7e3ee4846c7955ab8f84cf2b1, osmo-bsc sets its
  ICMI bit properly, but passes this test only because it *always* sends
  smod (start-mode) bits as zero.

- in I49691df01745a7c485bf165e897872c35fc4b147, the smod bits are
  properly sent on RSL, but this test shows that when ICMI becomes zero
  for 'start-mode auto', the smod bits will remain whatever start-mode
  was set in the previous osmo-bsc config. Instead, osmo-bsc should
  clear the smod bits for 'start-mode auto' so that its MultiRate Config
  does not vary depending on what was previously configured.

- in I1ec5bad0bce01cc425ee05ecf70c83ec662a226a, clearing smod is
  implemented and this test is expected to pass.

Change-Id: I151678f64e680f30f35b6bb2b0036d63efde9f2c
1 file changed