messaging_service: use correct value for listen_to_bc_address is a constructor used by tests
messaging_service: use correct value for listen_to_bc_address is a constructor used by tests

Also make sure to not listen on the same exact address twice in case
listen_address == broadcast_address. Scylla configuration code does not
allow such thing to be configured, but better to be safe.

Message-Id: <6ddebb91e84a7944fc2bae87e9d64d5a33f09457@scylladb.com>

scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,duarten/scylla,duarten/scylla,raphaelsc/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,raphaelsc/scylla