MEDIUM: log-forward: use "dgram-bind" instead of "bind" for the listener

MEDIUM: log-forward: use "dgram-bind" instead of "bind" for the listener

The use of "bind" wasn't that wise but was temporary. The problem is that
it will not allow to coexist with tcp. Let's explicitly call it "dgram-bind"
so that datagram listeners are expected here, leaving some room for stream
listeners later. This is the only change.