So that it is possible to try running enb on generated configs becuase
with previous numbers enb refuses to start:

    ~/enb# ./lteenb  x/old/enb.cfg
    ...
    x/old/enb.cfg:50: field 'dl_earfcn': range is [0:262143] (LTE Cell #0)

    ~/enb# ./lteenb  x/old/gnb.cfg
    ...
    x/old/gnb.cfg:54: invalid frequency band (NR Cell #1)

We need enb to be able to start with generated config because enb dumps in its
enb.log the real configuration that it builds from cell_list + cell_default and
nr_cell_list + cell_default - which is possible to extract via `json_util` and
which we want to check after our changes to enb.jinja2.cfg to see if we
really don't introduce semantic mistakes when e.g. moving things in between
cell_default to cell_list (see next patch).

With new frequencies enb and gnb both start ok.

/cc @lu.xu, @tomo, @xavier_thompson, @Daetalus
/reviewed-by @jhuge
/reviewed-on !1515