Settings: MSim: fix carrier name display

- The existing implementation displays the network name of the
  default SIM for both SIMs, which is simply incorrect
- Pass the subId to the function to get the value for the correct
  SIM
- Use the SIM name (instead of the network name), since the network
  name can be a different network when roaming
- If SIM name is empty (SPN not provided by carrier), display the
  network name if not roaming for better UX

Change-Id: I546dc952d7516579b763399f2d1f6db978163888