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

lib/classifier.c

@@ -83,6 +83,7 @@ cls_rule_init_exact(const struct flow *flow,
                     unsigned int priority, struct cls_rule *rule)
 {
     rule->flow = *flow;
+    rule->flow.priority = 0;
     flow_wildcards_init_exact(&rule->wc);
     rule->priority = priority;
 }