handover: intra-cell HO using Assignment cannot possibly work, "RR Assignment Complete" is factually ignored
Handover Decision algorithms may decide to do a re-assignment within the same cell.
In practical tests, some time ago, I noticed that using the RR Assignment Command wasn't working here.
Hence we currently send an RR Handover Command referencing the same cell, which is kind of weird.
Now I saw one reason why Assignment doesn't work for handover: in bsc_api.c, in handle_ass_compl(),
we receive the RR Assignment Complete message and dispatch an SS_LCHAN signal S_LCHAN_ASSIGNMENT_COMPL.
However, throughout osmo-bsc, there is not a single handler for S_LCHAN_ASSIGNMENT_COMPL.
This might be another casualty from the split-off from osmo-nitb.
Anyway, it doesn't make sense to me that we send an S_LCHAN_ASSIGNMENT_COMPL,
while the remaining code triggers bsc_subscr_conn_fsm.c GSCON_EV_* events directly.
Fix: Actually handle RR Assignment Complete during handover,
and send RR Assignment Command instead of RR Handover Command for intra-cell HO.
This is not high priority, and should wait until after intra-BSC handover has rippled through the lchan allocation code.