If a base station has multiple cells, it should be possible for UE to be handed
over from one cell into another, for example when UE crosses border of sectors.

So far we had only Inter-ENB HO and now we are also adding configuration for
HO in between all own cells.

Add tests for everything.

NOTE: we use allowed_meas_bandwidth, antenna_port_1 in dst=LTE case because
otherwise, e.g. for NR->LTE HO if they are not present, lteenb complains:

    enb.cfg:260: expecting 'allowed_meas_bandwidth' field
    enb.cfg:260: expecting 'antenna_port_1' field

for both Intra-ENB and Inter-ENB handovers.

For Intra-ENB case we can compute those numbers from cell definition. For
Inter-ENB case, when we don't know target context, we use conservative values.