net/sched: add sample action to the hardware intermediate representation

Add sample action to the hardware intermediate representation model which
would subsequently allow it to be used by drivers for offload.

Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>