handover_fsm: adjust inter-BSC HO failure handling to spec

Inter-BSC outgoing lacked the required BSSMAP HO Failure dispatch.

Not all cases should send BSSMAP HO Failure, name the relevant spec paragraphs
in comments and adjust handling.

Related: osmo-ttcn3-hacks If772dbbc5f9790d3f911465e1303dd0a99811154
Change-Id: I0980cacb9713e41a1eef3a0a7f6cc892e8a20da5
1 file changed