Osmux: Make sure all handover types work fine if a call leg is using Osmux between BSC and MSC.
It has never been tried and it could be it doesn't work.Let's add some TTCN3 tests to make sure we support different scenarios.
- intra-bsc handover between 2 BTS while BSC<->MSC is using Osmux
- inter-bsc handover between 1 BSC with osmux enabled and 1 BSC with osmux disabled while a call is ongoing. Test both handover directions (A->B, B->A).
- inter-msc handover between 2 MSC, one MSC having a BSC with Osmux enabled and another MSC having a BSC with Osmux disabled. Test both handover directions (A->B, B->A).