bsc: Update and add tests checking Last Used EUTRAN PLMN Id

CSFB indicator shouldn't be used as stated in the specs. Rather, BSC
should act based on "Last Used E-UTRAN PLMN Id" found in messages such
as Common Id, or Handover Request/Required.

Related: SYS#5337
Related: osmo-bsc.git Change-Id I5d290ac55eca5adde1c33396422f4c10b83c03d5
Change-Id: I7b2e5a3ad24c10e279a7f1c447804100168203ba
1 file changed