revalidator: Improve optimization to skip revalidation.
The should_revalidate() optimisation introduced with commit
698ffe3623
(revalidator: Only revalidate high-throughput flows.) was a little
aggressive, occasionally deleting flows even when OVS is quite capable
of performing full revalidation.
This commit modifies the logic to:
* Firstly, check if we are likely to handle full revalidation, and
attempt that instead.
* Secondly, fall back to the existing flow throughput estimations to
determine whether to revalidate the flow or just delete it.
VMware-BZ: #
1271926
Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Alex Wang <alexw@nicira.com>