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>

include/net/sock.h

@@ -59,6 +59,7 @@
 #include <linux/static_key.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
+#include <linux/cgroup-defs.h>
 
 #include <linux/filter.h>
 #include <linux/rculist_nulls.h>
@@ -308,8 +309,7 @@ struct cg_proto;
   *	@sk_send_head: front of stuff to transmit
   *	@sk_security: used by security modules
   *	@sk_mark: generic packet mark
-  *	@sk_cgrp_prioidx: socket group's priority map index
-  *	@sk_classid: this socket's cgroup classid
+  *	@sk_cgrp_data: cgroup data for this cgroup
   *	@sk_cgrp: this socket's cgroup-specific proto data
   *	@sk_write_pending: a write to stream socket waits to start
   *	@sk_state_change: callback to indicate change in the state of the sock
@@ -443,12 +443,7 @@ struct sock {
 #ifdef CONFIG_SECURITY
 	void			*sk_security;
 #endif
-#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)
-	u16			sk_cgrp_prioidx;
-#endif
-#ifdef CONFIG_CGROUP_NET_CLASSID
-	u32			sk_classid;
-#endif
+	struct sock_cgroup_data	sk_cgrp_data;
 	struct cg_proto		*sk_cgrp;
 	void			(*sk_state_change)(struct sock *sk);
 	void			(*sk_data_ready)(struct sock *sk);