Merge pull request #1498 from pijyoi/master

ZMQ_TCP_KEEPALIVE_IDLE doc wrongly says it overrides TCP_KEEPCNT

doc/zmq_setsockopt.txt

@@ -772,9 +772,9 @@ Default value:: -1 (leave to OS default)
 Applicable socket types:: all, when using TCP transports.
 
 
-ZMQ_TCP_KEEPALIVE_IDLE: Override TCP_KEEPCNT (or TCP_KEEPALIVE on some OS)
+ZMQ_TCP_KEEPALIVE_IDLE: Override TCP_KEEPIDLE (or TCP_KEEPALIVE on some OS)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Override 'TCP_KEEPCNT' (or 'TCP_KEEPALIVE' on some OS) socket option (where
+Override 'TCP_KEEPIDLE' (or 'TCP_KEEPALIVE' on some OS) socket option (where
 supported by OS). The default value of `-1` means to skip any overrides and
 leave it to OS default.