Previously, a switch would only notify the controller when flows expired.
Now, when a switch is told to delete flows, it sends a flow expiration
message, enabling the controller to get packet and byte counts from
deleted flows. Without this, the controller must retrieve flow statistics
and then delete the flow, during which time the counts could change. This
could also aid in debugging if multiple applications or programs
controlling the same switch are deleting each others' flows.
This commit adds a OFPER_DELETE as a choice for the reason field of a flow
expiration.
Brandon Heller
b5525791b5