private static class OFMessageDamper.DamperEntry
An entry in the TimedCache. A cache entry consists of the sent message
as well as the switch to which the message was sent.
NOTE: We currently use the full OFMessage object. To save space, we
could use a cryptographic hash (e.g., SHA-1). However, this would
obviously be more time-consuming....
We also store a reference to the actual IOFSwitch object and /not/
the switch DPID. This way we are guaranteed to not dampen messages if
a switch disconnects and then reconnects.