gateway: httpgateway: Adjust default payload length for urlencoded content

gateway/httpgateway.h

@@ -1,5 +1,8 @@
 #ifndef HTTPGATEWAY_H
 #define HTTPGATEWAY_H
+
+#define CPPHTTPLIB_FORM_URL_ENCODED_PAYLOAD_MAX_LENGTH 65536
+
 #include <httplib.h>
 #include "gatewayinterface.h"
 #include "../requestworker.h"