verify that legacy handover configuration still works after introduction of inter-BSC HO support
The legacy handover configuration is that all ARFCNs used by any BTS are indicated as neighbor ARFCNs for all cells.
The OsmoBSC manual claims that this still works as long as no new-style 'neighbor' config is present in the .cfg file.
Indeed, generate_bcch_chan_list() in osmo-bsc/src/osmo-bsc/system_information.c adds all cells' ARFCNs to the neighbors list that is advertised to BTS,MS.
With a test, verify that an actual handover procedure indeed picks up such an implicit target cell.
Not only that the ARFCN gets listed in SI2 as neighbor, but also that if a handover decision kicks in, such an implicit neighbor cell is found as a target in handover_start(), and the handover procedure indeed is followed through.
(If it doesn't work, handover_start() would complain with "neighbor unknown")