[TCP]: Add tcp_for_write_queue_from_safe and use it in mtu_probe

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index cdd0050..6e392ba 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1229,6 +1229,11 @@
 		for (; (skb != (struct sk_buff *)&(sk)->sk_write_queue);\
 		     skb = skb->next)
 
+#define tcp_for_write_queue_from_safe(skb, tmp, sk)			\
+		for (tmp = skb->next;					\
+		     (skb != (struct sk_buff *)&(sk)->sk_write_queue);	\
+		     skb = tmp, tmp = skb->next)
+
 static inline struct sk_buff *tcp_send_head(struct sock *sk)
 {
 	return sk->sk_send_head;