udp_outgoing_address is used for UDP packets sent out to other
caches.
The default behavior is to not bind to any specific address.
Instead it will use the same socket as udp_incoming_address.
Only change this if you want to have UDP queries sent using another
address than where this Squid listens for UDP queries from other
caches.
NOTE: udp_outgoing_address is used by the ICP, HTCP, and DNS
modules. Altering it will affect all of them in the same manner.
see also; udp_incoming_address
NOTE, udp_incoming_address and udp_outgoing_address can not
have the same value since they both use the same port.