fix espconn and err_t (#5392)

Author: d-a-v

Diff for: tools/sdk/include/espconn.h

@@ -29,7 +29,12 @@
 extern "C" {
 #endif
 
-typedef sint8 err_t;
+//typedef sint8 err_t;
+// err_t has been redefined by espressif,
+// use autogenerated <lwip-err-t.h> to define LWIP_ERR_T,
+// this is compatible with both versions of lwIP.
+#include <../../lwip2/include/lwip-err-t.h>
+#include <lwip/err.h>
 
 typedef void *espconn_handle;
 typedef void (* espconn_connect_callback)(void *arg);