multi-ARFCN: fix maximum number of carriers limitation

Maximum number of carriers is fixed to 3 channels on a single
physical RF channel in multi-ARFCN mode. For some reason, it
was limited to 5.

Let's fix this, and also follow this limitation in the
following VTY command handlers:

  - cfg_multi_arfcn_cmd,
  - cfg_chan_cmd.

Change-Id: I66a1462f368458afd313ee6f0bc0abc496dde817
3 files changed