net: give better error messages

Add address and/or port to errors where applicable for better reporting.

See #7005
Doing two checks for `port`. I'd change it to the following:
```javascript
var additions = {
  address: address
};
var details;
if (port) {
  details = util.format('%s:%s', address, port);
  additions.port = port;
} else {
  details = address;
}
```