net: #ifdefify sk_classid member of struct sock

The sk_classid member is only required when CONFIG_CGROUP_NET_CLASSID is
enabled. #ifdefify it to reduce the size of struct sock on 32 bit
systems, at least.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -429,7 +429,9 @@ struct sock {
 	void			*sk_security;
 #endif
 	__u32			sk_mark;
+#ifdef CONFIG_CGROUP_NET_CLASSID
 	u32			sk_classid;
+#endif
 	struct cg_proto		*sk_cgrp;
 	void			(*sk_state_change)(struct sock *sk);
 	void			(*sk_data_ready)(struct sock *sk);

net/netfilter/nft_meta.c

@@ -166,11 +166,13 @@ void nft_meta_get_eval(const struct nft_expr *expr,
 			goto err;
 		*dest = out->group;
 		break;
+#ifdef CONFIG_CGROUP_NET_CLASSID
 	case NFT_META_CGROUP:
 		if (skb->sk == NULL || !sk_fullsock(skb->sk))
 			goto err;
 		*dest = skb->sk->sk_classid;
 		break;
+#endif
 	default:
 		WARN_ON(1);
 		goto err;
@@ -246,7 +248,9 @@ int nft_meta_get_init(const struct nft_ctx *ctx,
 	case NFT_META_CPU:
 	case NFT_META_IIFGROUP:
 	case NFT_META_OIFGROUP:
+#ifdef CONFIG_CGROUP_NET_CLASSID
 	case NFT_META_CGROUP:
+#endif
 		len = sizeof(u32);
 		break;
 	case NFT_META_IIFNAME: