Fix bug #55078: Add custom data to pbuf struct

Add a #define that users can use to store custom data on a pbuf

(cherry picked from commit 92a18bf6382077c88b11126b1e662dfb5386e637)

src/include/lwip/opt.h

@@ -1555,6 +1555,14 @@
 #if !defined LWIP_PBUF_REF_T || defined __DOXYGEN__
 #define LWIP_PBUF_REF_T                 u8_t
 #endif
+
+/**
+ * LWIP_PBUF_CUSTOM_DATA: Store private data on pbufs (e.g. timestamps)
+ * This extends struct pbuf so user can store custom data on every pbuf.
+ */
+#if !defined LWIP_PBUF_CUSTOM_DATA || defined __DOXYGEN__
+#define LWIP_PBUF_CUSTOM_DATA
+#endif
 /**
  * @}
  */

src/include/lwip/pbuf.h

@@ -219,6 +219,9 @@ struct pbuf {
 
   /** For incoming packets, this contains the input netif's index */
   u8_t if_idx;
+
+  /** In case the user needs to store data custom data on a pbuf */
+  LWIP_PBUF_CUSTOM_DATA
 };