sflow: Export OVS datapath performance counters via sFlow.
The OVS cache hit/miss counters and memory/CPU usage statistics have been
identified as important metrics when managing large deployments. This patch
allows them to be pushed periodically as part of the sFlow feed, and
represents a more efficient and scalable alternative to polling via
ovs-dpctl(1).
Signed-off-by: Neil McKee <neil.mckee@inmon.com> Signed-off-by: Ben Pfaff <blp@nicira.com>