datapath-windows: Change reported time for flows

datapath-windows: Change reported time for flows

Currently the datapath reports the tick counter to the userspace.
The userspace uses KeQueryPerformanceCounter as a monotonic clock.

This patch changes the flow stats to be reported in a monotonic format, while
also decaying the time between the flow actual usage and the flow report usage.

This patch also changes to report EEXIST if the userspace tries to add the same
flow twice.

After adding a flow, lookup the flow only if the extension is compiled in debug
mode.

Signed-off-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Acked-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>