Work done by Thomas Graf <tgraf@suug.ch> and
Jamal Hadi Salim <hadi@cyberus.ca>

The following patchset introduces generic network statistics for
netlink users. It uses nested TLV which prevents further compatibility
problems when introducing new statistics. Backward compatibility to
existing TLV types TCA_STATS and TCA_XSTATS is ensured but can be
easly removed once it is no longer needed. Therefore prior users of
struct tc_stats can be converted to this API and existing userspace
applications will not notice a difference while converted applications
can use the new extendable statistic interface.

Changes:
- Add generic network statistics API for netlink users.
- Introduces a generic rate estimator based on timers. Patch is based
  on Jamals patch and adapted to the new generic network statistics
  API.
- Add documentation of generic network statistics and estimator API.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>