rewrite subscriber_update_notify() without calls into luop

This function relied on implementation details of the luop code.
Port what is necessary for an independent Insert Subscriber Data
Tx operation from the luop code into this function.

A next possible step would be to try to merge both of these
into a common implementation. This will be addressed in a
follow-up change as soon as this change is merged.

The TTCN3 test TC_vty_msisdn_isd is still passing (it currently
triggers the "circuit switched domain" case because it does not
advertise itself as an SGSN in the IPA unit name).

Change-Id: I06c43ece2b48dc63d599000eb6d6d51e08963067
Related: OS#2785
4 files changed