Merge pull request #3727 from Botje/fix-poller-example

Problem: Poller example has wrong argument order

RELICENSE/Botje.md

+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Dries Harnie
+that grants permission to relicense its copyrights in the libzmq C++
+library (ZeroMQ) under the Mozilla Public License v2 (MPLv2) or any other 
+Open Source Initiative approved license chosen by the current ZeroMQ 
+BDFL (Benevolent Dictator for Life).
+
+A portion of the commits made by the Github handle "Botje", with
+commit author "Dries Harnie <dries@harnie.be>", are copyright of Dries Harnie.
+This document hereby grants the libzmq project team to relicense libzmq, 
+including all past, present and future contributions of the author listed above.
+
+Dries Harnie
+2019/10/31

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);