Ad MGW / MGCP Emulation to TTCN-3 testsuite for BSC
Right now, the BSC tests in TTCN-3 test a combination of BSC+MGW, which means that the MGCP protocol is not exposed to the tester. This means we cannot validate MGCP and e.g. cause CRCX / MDCX to fail in a controlled way to test error paths in OsmoBSC.
Let's implement a MGCP_Emulation that exists on the same level as the RSL_Emulation and BSSAP_Emulation, so that from a single test case we can speak to all relevant interfaces.