fix MSC.TC_lu_clear_request: allow LU Reject, forbid 2nd Clear Cmd

When the MS sends a Clear Request in the middle of a Location Updating, it
should be permitted for the MSC to send a Location Updating Reject back. Extend
with an alt that also allows a LU reject before the Clear Command.

The test explicitly hints at https://osmocom.org/issues/2862 which rightfully
forbids the MSC to send a second Clear Command after the first is completed.
However, this test so far explicitly permits a second Clear Command, so it was
probably passing in error all the time. Set verdict to failure if a second
Clear Command is received before the DISC_IND.

This changes the test verdict to failure with current osmo-msc master,
rightfully so; the failure will be fixed by the upcoming MSC subscr conn FSM
refactoring.

Change-Id: I7bc5555b829d61b0a2529107bc9b58446865545d
2 files changed