In the inter-BSC 'Handover Required', do not send a LAI cell identifier,
but a CGI one.
Rationale:
As explained in OS#5188, 3GPP TS 48.008 allows a LAI identification only
in the Cell Identifier List IE, but not in the single Cell Identifier
IE.
In the inter-BSC HO test's Handover Required message, we so far send a
LAI identifier in a List IE to osmo-msc. And so far, osmo-msc simply
echos that in the Handover Request message's single Cell Id IE.
The LAI is, as actually defined in the spec, omitted from the single IE
in deps/titan.ProtocolModules.BSSMAP/src/BSSAP_Types.ttcn, and when
osmo-msc sends the non-standard LAI Id, ttcn3 fails to parse the BSSMAP
Handover Request message: the Cell Identifier IE gets wrong values, and
all remaining IEs are parsed as 'omit' even though they are present on
the wire. So as long as osmo-msc sends back a LAI Id, we cannot sanely
verify the Handover Request received from the MSC.
The CGI identifier type is supported in both IEs. So when the test sends
a CGI identifier in the Handover Required, osmo-msc will also reflect a
CGI identifier in the Handover Request, and ttcn3 parsing works.
This prepares for adding verification of the ciphering in inter-BSC
handover, in turn a preparation for adding tests of A5/4.
Related: OS#5188 SYS#5324
Change-Id: I48276acf923626db171683dfa03ef43614a71380
2822d07ab2