net: destroy socket on DNS error

The socket was never destroyed on DNS errors. This broke some clients, including
lib/https.js.

lib/net.js

@@ -570,6 +570,7 @@ Socket.prototype.connect = function(port /* [host], [cb] */) {
         // error event to the next tick.
         process.nextTick(function() {
           self.emit('error', err);
+          self.destroy();
         });
       } else {
         timers.active(self);