Problem: zmq_poller example is wrong

Solution: flipped arguments in example

doc/zmq_poller.txt

@@ -264,9 +264,9 @@ void *poller = zmq_poller_new ();
 
 zmq_poller_event_t events [2];
 /* First item refers to 0MQ socket 'socket' */
-zmq_poller_add (poller, socket, ZMQ_POLLIN, NULL);
+zmq_poller_add (poller, socket, NULL, ZMQ_POLLIN);
 /* Second item refers to standard socket 'fd' */
-zmq_poller_add_fd (poller, fd, ZMQ_POLLIN, NULL);
+zmq_poller_add_fd (poller, fd, NULL, ZMQ_POLLIN);
 /* Poll for events indefinitely */
 int rc = zmq_poller_wait_all (items, events, 2, -1);
 assert (rc >= 0);