tc: add dualpi2 scheduler module

tc: add dualpi2 scheduler module

DUALPI2 AQM is a combination of the DUALQ Coupled-AQM with a PI2
base-AQM. The PI2 AQM is in turn both an extension and a simplification
of the PIE AQM. PI2 makes quite some PIE heuristics unnecessary, while
being able to control scalable congestion controls like TCP-Prague.
With PI2, both Reno/Cubic can be used in parallel with Prague,
maintaining window fairness. DUALQ provides latency separation between
low latency Prague flows and Reno/Cubic flows that need a bigger queue.

This patch adds support to tc to configure it through its netlink
interface.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Co-developed-by: Olga Albisser <olga@albisser.org>
Signed-off-by: Olga Albisser <olga@albisser.org>
Co-developed-by: Koen De Schepper <koen.de_schepper@nokia-bell-labs.com>
Signed-off-by: Koen De Schepper <koen.de_schepper@nokia-bell-labs.com>
Co-developed-by: Oliver Tilmans <olivier.tilmans@nokia.com>
Signed-off-by: Oliver Tilmans <olivier.tilmans@nokia.com>
Signed-off-by: Bob Briscoe <research@bobbriscoe.net>
Co-developed-by: Henrik Steen <henrist@henrist.net>
Signed-off-by: Henrik Steen <henrist@henrist.net>
Reviewed-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>