datapath: Convert kernel priority actions into match/set.

datapath: Convert kernel priority actions into match/set.

Following patch adds skb-priority to flow key. So userspace will know
what was priority when packet arrived and we can remove the pop/reset
priority action. It's no longer necessary to have a special action for
pop that is based on the kernel remembering original skb->priority.
Userspace can just emit a set priority action with the original value.

Since the priority field is a match field with just a normal set action,
we can convert it into the new model for actions that are based on
matches.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>
Bug #7715