bsc: Test MGCP-over-IPA forwarding in SCCPlite tests

* MGCP-over-IPA handling in MSC_ConnectionHandler means we need to use
the new MGCP_CLIENT_MULTI port since we'll be managing MGCP messages
from 2 different UDP connections, and we need to be able to route
answers correctly. As a result, parameter multi_conn_mode is enabled for
SCCPlite and all code adapted to use that port in that type of scenario.
* iDuring calls when on SCCPlite, send a full (all-required-params-in)
CRCX through the MGCP-over-IPA connection towards the BSC in order to
emulate the MSC, and expect the correct answer back. This way we test
BSC funcionality to forward MGCP messages coming from MSC works as
expected.

Related: OS#2536
Depends: osmo-bsc.git I38ad8fa645c08900e0e1f1b4b96136bc6d96b3ab
Change-Id: I31fed700772dd0b063f913b1e1639fd428c46e7d
2 files changed