PCUIF: Prepare for simulating BTS side of PCU Interface

Our TTCN-3 PCUIF code so far was only used to simulate the PCU side
of the interface: connecting to the socket as a client.  However,
it's also useful to emulate the BTS side of the interface: Listening
for a connection as a server.

Also, the send/receive templates are prepared for the inverse role.

Change-Id: I779ff2903cab8c13ffb8fe10a4cacd996bafe69a
2 files changed