Set UDP datagram source address (ticket #1239). Previously, the source IP address of a response UDP datagram could differ from the original datagram destination address. This could happen if the server UDP socket is bound to a wildcard address and the network interface chosen to output the response packet has a different default address than the destination address of the original packet. For example, if two addresses from the same network are configured on an interface. Now source address is set explicitly if a response is sent for a server UDP socket bound to a wildcard address.