improve failure diagnostics in TC_vty_msisdn_isd HLR test

Check for reception of an Insert Subscriber Data with outdated MSISDN.
This happened to me while working on a fix for issue OS#2785, and it
seems to be an easy mistake implementations can make. Catch this
situation in the test and log an explicit message about the problem.

Related: OS#2785
Change-Id: Ib0809617cca621cc22f29b078828057fd49f27e5
1 file changed