fix issue 10: incorrect calculation in ip6 of transport layer chksum. reported by avkulkarni.
fix issue 10: incorrect calculation in ip6 of transport layer chksum. reported by avkulkarni.

git-svn-id: c24decc6cc9e43397d358c131c6d3542a5bd9019@50 30ee8f51-df1a-0410-9115-614dbba9287e

asteven/dpkt