* BSSGP_Emulation: dont fail when removing a non-exitent client
* BSSGP_Emulation: remove unused BSSGP_SP.receive(PDU_L3_MS_SGSN)
* BSSGP_Emulation: move LLC layer out of BSSGP
* BSSGP_Emulation: add type record LLC_Entities
* sgsn: add f_cellid_to_RAI()
* sgsn: introduce TC_attach_rau_a_a()
* sgsn: introduce f_routing_area_update()
* sgsn: create 3 instances of BSSGP at the same time
* BSSGP_Emulation.ttcn: extend BSSGP_Client_CT to hold 3 instances of BSSGP
