net: pack skb_shared_info more efficiently

nr_frags can be 8 bits since 256 is plenty of fragments. This allows it to be
packed with tx_flags.

Also by moving ip6_frag_id and dataref (both 4 bytes) next to each other we can
avoid a hole between ip6_frag_id and frag_list on 64 bit systems.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -242,15 +242,15 @@ struct ubuf_info {
  * the end of the header data, ie. at skb->end.
  */
 struct skb_shared_info {
-	unsigned short	nr_frags;
+	unsigned char	nr_frags;
+	__u8		tx_flags;
 	unsigned short	gso_size;
 	/* Warning: this field is not always filled in (UFO)! */
 	unsigned short	gso_segs;
 	unsigned short  gso_type;
-	__be32          ip6_frag_id;
-	__u8		tx_flags;
 	struct sk_buff	*frag_list;
 	struct skb_shared_hwtstamps hwtstamps;
+	__be32          ip6_frag_id;
 
 	/*
 	 * Warning : all fields before dataref are cleared in __alloc_skb()