Fix natpmp request issue on Windows

Author: happyharryh

ext/libnatpmp/natpmp.c

@@ -39,12 +39,8 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <winsock2.h>
 #include <ws2tcpip.h>
 #include <io.h>
-#ifndef EWOULDBLOCK
 #define EWOULDBLOCK WSAEWOULDBLOCK
-#endif
-#ifndef ECONNREFUSED
 #define ECONNREFUSED WSAECONNREFUSED
-#endif
 #include "wingettimeofday.h"
 #define gettimeofday natpmp_gettimeofday
 #else