Don't show time stamp-based information if we don't have it (now that we

Don't show time stamp-based information if we don't have it (now that we
know whether packets - or "packets" - have time stamps).

Show the time stamp order as "Unknown" if we don't have enough
information to determine whether it's certainly in order or out of order
(XXX - we should do that if we have only one packet that has a time stamp).

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@41186 f5534014-38df-0310-8fa8-9805f1628bb7