We never want to listen on port 0, even if configured so.
When the listen port is set to 0, the OS will choose the
port randomly, which makes it useless for communicating
with other nodes in the cluster, since we don't support that.
Also, it causes the listen_ports_conf_test internode_ssl_test
to fail since it expects to disable listening on storage_port
or ssl_storage_port when set to 0, as seen in
https://github.com/scylladb/scylla-dtest/issues/2174.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>