net: unset IFF_XMIT_DST_RELEASE in ipgre_tunnel_setup()

ipgre_tunnel_xmit() might need skb->dst, so tell dev_hard_start_xmit()
to no release it.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_gre.c

@@ -1238,6 +1238,7 @@ static void ipgre_tunnel_setup(struct net_device *dev)
 	dev->iflink		= 0;
 	dev->addr_len		= 4;
 	dev->features		|= NETIF_F_NETNS_LOCAL;
+	dev->priv_flags		&= ~IFF_XMIT_DST_RELEASE;
 }
 
 static int ipgre_tunnel_init(struct net_device *dev)