net: wrap sock->sk_cgrp_prioidx and ->sk_classid inside a struct

Introduce sock->sk_cgrp_data which is a struct sock_cgroup_data.
->sk_cgroup_prioidx and ->sk_classid are moved into it.  The struct
and its accessors are defined in cgroup-defs.h.  This is to prepare
for overloading the fields with a cgroup pointer.

This patch mostly performs equivalent conversions but the followings
are noteworthy.

* Equality test before updating classid is removed from
  sock_update_classid().  This shouldn't make any noticeable
  difference and a similar test will be implemented on the helper side
  later.

* sock_update_netprioidx() now takes struct sock_cgroup_data and can
  be moved to netprio_cgroup.h without causing include dependency
  loop.  Moved.

* The dummy version of sock_update_netprioidx() converted to a static
  inline function while at it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/cls_cgroup.h b/include/net/cls_cgroup.h
index ccd6d8b..c0a92e2 100644
--- a/include/net/cls_cgroup.h
+++ b/include/net/cls_cgroup.h
@@ -41,13 +41,12 @@
 	return classid;
 }
 
-static inline void sock_update_classid(struct sock *sk)
+static inline void sock_update_classid(struct sock_cgroup_data *skcd)
 {
 	u32 classid;
 
 	classid = task_cls_classid(current);
-	if (classid != sk->sk_classid)
-		sk->sk_classid = classid;
+	sock_cgroup_set_classid(skcd, classid);
 }
 
 static inline u32 task_get_classid(const struct sk_buff *skb)
@@ -64,17 +63,17 @@
 	 * softirqs always disables bh.
 	 */
 	if (in_serving_softirq()) {
-		/* If there is an sk_classid we'll use that. */
+		/* If there is an sock_cgroup_classid we'll use that. */
 		if (!skb->sk)
 			return 0;
 
-		classid = skb->sk->sk_classid;
+		classid = sock_cgroup_classid(&skb->sk->sk_cgrp_data);
 	}
 
 	return classid;
 }
 #else /* !CONFIG_CGROUP_NET_CLASSID */
-static inline void sock_update_classid(struct sock *sk)
+static inline void sock_update_classid(struct sock_cgroup_data *skcd)
 {
 }