fib: add flag to mark RPL routes

sys/include/net/fib.h

@@ -62,6 +62,11 @@ typedef struct fib_destination_set_entry_t {
  */
 #define FIB_LIFETIME_NO_EXPIRE (0xFFFFFFFFffffffff)
 
+/**
+ * @brief flag to identify if a route was set by RPL
+ */
+#define FIB_FLAG_RPL_ROUTE (1UL << 0)
+
 /**
  * @brief initializes all FIB entries with 0
  *