sgsn: test umts aka with gsm sres response

Add ability to test UMTS AKA, by f_gmm_attach() with flags to select UMTS AKA
and to respond to it with GSM AKA SRES.

Add TC_attach_umts_aka_umts_res and TC_attach_umts_aka_gsm_sres.

Change existing TC_attach_* to also call f_gmm_attach(). (Actually,
f_gmm_attach() is almost exactly the previous TC_attach function body.)

osmo-sgsn change I36807bad3bc55c0030d4f09cb2c369714f24bec7 will implement
proper handling of GSM AKA response and make TC_attach_umts_aka_gsm_sres pass.

Related: OS#3193 OS#3224
Change-Id: I201ffeaee4439a413ab8289aceeccca9aba40a7a
3 files changed