EAFNOSUPPORT defined on Windows platform

Windows headers don't defined this error.
This patch defines it if not already defined.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

include/zmq.h

@@ -101,6 +101,9 @@ ZMQ_EXPORT void zmq_version (int *major, int *minor, int *patch);
 #ifndef ENOTSOCK
 #define ENOTSOCK (ZMQ_HAUSNUMERO + 9)
 #endif
+#ifndef EAFNOSUPPORT
+#define EAFNOSUPPORT (ZMQ_HAUSNUMERO + 10)
+#endif
 
 /*  Native 0MQ error codes.                                                   */
 #define EFSM (ZMQ_HAUSNUMERO + 51)

src/err.cpp

@@ -228,6 +228,9 @@ void zmq::wsa_error_to_errno ()
     case WSAEADDRNOTAVAIL:
         errno = EADDRNOTAVAIL;
         return;
+    case WSAEAFNOSUPPORT:
+        errno = EAFNOSUPPORT;
+        return;
     default:
         wsa_assert (false);
     }