vlr: fix GSM AKA in a UMTS AKA capable environment

Switch by vsub->sec_ctx to use the proper Kc for ciphering.

Even on an R99 capable MS with a UMTS AKA capable USIM, the MS may still choose
to only perform GSM AKA, as long as the bearer is GERAN. The VLR already stores
whether the MS replied with a GSM AKA SRES or a UMTS AKA RES in vsub->sec_ctx.
So far, though, we were always using the UMTS AKA Kc just because the USIM and
core net are capable of it, ignoring the choice the MS might have made in the
Authentication Response.

In msc_vlr_test_gsm_ciph, fix the test expectations to the correct GSM AKA Kc
keys, showing that all of LU, CM Service Request and Paging Response now
support MS choosing GSM AKA in a UMTS capable environment.

Related: OS#2793
Change-Id: I42ce51ae979f42d173a45ae69273071c426bf97c
4 files changed