ppp: unset IFF_XMIT_DST_RELEASE in ppp_setup()

Jarek pointed pppoe can call back dev_queue_xmit(), and might need
skb->dst, so its safer to unset IFF_XMIT_DST_RELEASE on ppp devices.
Signed-off-by: NEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ppp_generic.c

@@ -1054,6 +1054,7 @@ static void ppp_setup(struct net_device *dev)
 	dev->type = ARPHRD_PPP;
 	dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
 	dev->features |= NETIF_F_NETNS_LOCAL;
+	dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
 }
 
 /*