[ovs-dev] simple implementation of interface statistics in OVSDB

[Ben Pfaff]

This patch series implements a simpler version of OVSDB database
statistics than the RFC I sent out a few days ago.  Instead of
adding a new protocol to update statistics on demand, it just
refreshes interface statistics every 5 seconds.  I'm continuing to
work on implementing the more advanced approach, but this series
seems like a good place to start.