Changes

SGSN: f_TC_attach_timeout_after_pdp_act: allow authentication

While testing, allow the SGSN to authenticate the UE.
The new VLR code will authenticate the UE, while
the old code doesn't.
The test case TC_attach_timeout_after_pdp_act doesn't is testing if the
PDP context is correctly timedout.

Change-Id: I11c628ecebbe7c4c1b2c28e63133a33cfc171e12