ppp: Use skb_queue_walk() in ppp_mp_insert().

Instead of open-coded version.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ppp_generic.c

@@ -1863,9 +1863,10 @@ ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb)
 
 	/* N.B. we don't need to lock the list lock because we have the
 	   ppp unit receive-side lock. */
-	for (p = list->next; p != (struct sk_buff *)list; p = p->next)
+	skb_queue_walk(list, p) {
 		if (seq_before(seq, p->sequence))
 			break;
+	}
 	__skb_queue_before(list, p, skb);
 }