The spec permits RAB AssignmentRequests with multiple RABs at a time.
Even though one voice call is assigned only one RAB in practice. Since
the current FSM implementation only supports a 1:1 scenario, lets check
if the MSC really assigns only one RAB and block RAB Assignments that do
not fit in this scheme.
Change-Id: I0f1d868fd0b4dc413533d6fcc5482862825181be
Related: OS#5152