ppp: avoid false drop_monitor false positives

Call consume_skb() in place of kfree_skb() were appropriate.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ppp/ppp_async.c

@@ -613,7 +613,7 @@ ppp_async_encode(struct asyncppp *ap)
 	*buf++ = PPP_FLAG;
 	ap->olim = buf;
 
-	kfree_skb(ap->tpkt);
+	consume_skb(ap->tpkt);
 	ap->tpkt = NULL;
 	return 1;
 }