sgsn: add TC_attach_gmm_attach_req_while_gmm_attach

Testing the corner case of receiving an Attach Request
while not (yet) sent an Attach Accept.

MS -> SGSN: Attach Request IMSI
MS <- SGSN: Identity Request IMSI (optional)
MS -> SGSN: Identity Response IMSI (optional)
MS <- SGSN: Identity Request IMEI
MS -> SGSN: Attach Request (2nd)
MS <- SGSN: Identity Response IMEI
MS <- SGSN: Attach Accept
MS -> SGSN: Attach Complete

Change-Id: I0bac50dc5a72ba8f9010b05bcb98aa7ff0b81cf6
1 file changed