fix gre parser infinite loop. we should throw an exception on malformed sres instead of spinning forever. bug filed in person by jon larimer.
fix gre parser infinite loop. we should throw an exception on malformed sres instead of spinning forever. bug filed in person by jon larimer.

git-svn-id: c24decc6cc9e43397d358c131c6d3542a5bd9019@75 30ee8f51-df1a-0410-9115-614dbba9287e

asteven/dpkt