[NET]: Reduce size of sk_buff by 4 bytes

Reduce local_df to a bit field and ip_summed to a 2 bits
field thus saving 13 bits. Move bit fields, packet type,
and protocol into the spare area between the priority
and the destructor. Saves 4 bytes on both, 32bit and
64bit architectures.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -248,13 +248,14 @@ struct sk_buff {
 				data_len,
 				mac_len,
 				csum;
-	unsigned char		local_df,
-				cloned:1,
-				nohdr:1,
-				pkt_type,
-				ip_summed;
 	__u32			priority;
-	unsigned short		protocol;
+	__u8			local_df:1,
+				cloned:1,
+				ip_summed:2,
+				nohdr:1;
+				/* 3 bits spare */
+	__u8			pkt_type;
+	__u16			protocol;
 
 	void			(*destructor)(struct sk_buff *skb);
 #ifdef CONFIG_NETFILTER