ppp: Remove direct skb_queue_head list pointer access.

Add a helper, __skb_peek(), and use it in ppp_mp_reconstruct().

Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1592,6 +1592,17 @@ static inline struct sk_buff *skb_peek(const struct sk_buff_head *list_)
 	return skb;
 }
 
+/**
+ *	__skb_peek - peek at the head of a non-empty &sk_buff_head
+ *	@list_: list to peek at
+ *
+ *	Like skb_peek(), but the caller knows that the list is not empty.
+ */
+static inline struct sk_buff *__skb_peek(const struct sk_buff_head *list_)
+{
+	return list_->next;
+}
+
 /**
  *	skb_peek_next - peek skb following the given one from a queue
  *	@skb: skb to start from