task #10495: Added support for IP_MULTICAST_LOOP at socket- and raw-API level.

src/include/lwip/pbuf.h

@@ -67,6 +67,8 @@ typedef enum {
 /** indicates this is a custom pbuf: pbuf_free and pbuf_header handle such a
     a pbuf differently */
 #define PBUF_FLAG_IS_CUSTOM 0x02U
+/** indicates this pbuf is UDP multicast to be looped back */
+#define PBUF_FLAG_MCASTLOOP 0x04U
 
 struct pbuf {
   /** next pbuf in singly linked pbuf chain */

src/include/lwip/udp.h

@@ -63,9 +63,10 @@ PACK_STRUCT_END
 #  include "arch/epstruct.h"
 #endif
 
-#define UDP_FLAGS_NOCHKSUM 0x01U
-#define UDP_FLAGS_UDPLITE  0x02U
-#define UDP_FLAGS_CONNECTED  0x04U
+#define UDP_FLAGS_NOCHKSUM       0x01U
+#define UDP_FLAGS_UDPLITE        0x02U
+#define UDP_FLAGS_CONNECTED      0x04U
+#define UDP_FLAGS_MULTICAST_LOOP 0x08U
 
 struct udp_pcb;