Use actual payload length to construct inner PDU. (#179)

Fixes #178

include/tins/ipv6.h

@@ -89,6 +89,15 @@ public:
         NO_NEXT_HEADER = 59
     };
 
+    /**
+     * The values used to identify Hop-By-Hop Options and Destination Options.
+     */
+    enum OptionType {
+        PAD_1 = 0,
+        PAD_N = 1,
+        JUMBO_PAYLOAD = 0xC2,
+    };
+
     /**
      * \brief Extracts metadata for this protocol based on the buffer provided
      *