add include of netx dns header

Author: JacobBarthelmeh

examples/mqttnet.c

@@ -383,6 +383,11 @@ static int NetRead(void *context, byte* buf, int buf_len,
 /* -------------------------------------------------------------------------- */
 #elif defined(HAVE_NETX)
 
+#ifndef WOLFMQTT_NO_NETX_DNS
+    /* include the NetX DNS addon header */
+    #include "nxd_dns.h"
+#endif
+
 static int NetDisconnect(void *context)
 {
     SocketContext *sock = (SocketContext*)context;