MSC_Tests.ttcn: correct VTY command in TC_lu_and_ss_session_timeout

The I3e1791773d56617172ae27a46889a1ae4d400e2f was merged before
the Icf4d87c45e90324764073e8230e0fb9cb96dd9cb, and there were a
few corrections of the VTY command format.

Change-Id: Icd1133ca9f46bc2a9302deebb1e401862cf672cb
1 file changed