BSSMAP: reject Level 3 Complete from cells with invalid LAI
Level 3 Complete messages contain a cell identity of the calling BSC/RNC.
For some time, in bssmap_rx_l3_compl(), we decoded that cell's PLMN, but never used it for anything.
Since https://gerrit.osmocom.org/#/c/7281/ we reject cell identities containing a PLMN mismatching the global network PLMN.
- Write a ttcn3 test that sends a LU from a BSC (A-interface, BSSMAP) that has a LAI mismatching the MSC's global PLMN.
(This issue is created as a split of #2980, to clarify the confusion we created there.)