MME_Tests: Add S11/GTPv2 interface

The S11 interface is used by the MME to talk to the SGW-C. At the moment
we do not simulate the S11 interface in our testcases. This is in particular
a problem for TC_s1ap_attach, which needs to answer the Create Session
Request, comming from the MME in order to continue.

As a first step, lets add evrything that is required to run an S11
interface in the testsuite.

Change-Id: I545dd6cef3cef7283f2e04c2406a2703c2fdd01a
Related: OS#5760
3 files changed