[NET]: Reduce size of struct sk_buff on 64 bit architectures

Move skb->nf_mark next to skb->tc_index to remove a 4 byte hole between
skb->nfmark and skb->nfct and another one between skb->users and skb->head
when CONFIG_NETFILTER, CONFIG_NET_SCHED and CONFIG_NET_CLS_ACT are enabled.
For all other combinations the size stays the same.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -270,14 +270,14 @@ struct sk_buff {
 
 	void			(*destructor)(struct sk_buff *skb);
 #ifdef CONFIG_NETFILTER
-	__u32			nfmark;
 	struct nf_conntrack	*nfct;
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
 	struct sk_buff		*nfct_reasm;
 #endif
 #ifdef CONFIG_BRIDGE_NETFILTER
 	struct nf_bridge_info	*nf_bridge;
 #endif
+	__u32			nfmark;
 #endif /* CONFIG_NETFILTER */
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */