Use TailQ in mbuf

include/ucore/mbuf.h

@@ -2,6 +2,7 @@
 #define UC_MBUF_H_
 #include <stdint.h>
 #include <stddef.h>
+#include "tailq.h"
 
 #ifdef __GNUC__
 #   define UC_INLINE inline __attribute__((always_inline))
@@ -17,9 +18,9 @@ enum UC_MBUF_FLAGS {
 };
 
 struct MBuf {
-    /** prev/next pointer, user can use this for a linked list*/
-    struct MBuf *prev;
-    struct MBuf *next;
+    /** linked list entry for keeping the mbufs in a list*/
+    struct TailQ entry;
+
     /** Pointers the user can use to remember spots in
      * the data. (these must either be NULL pointers or point into
      * something in the buffer*/