The tc could return NET_XMIT_CN as one congestion notification, but
it does not mean the packe is lost. Other modules like ipvlan,
macvlan, and others treat NET_XMIT_CN as success too.
So l2tp_eth_dev_xmit should add the NET_XMIT_CN check.
Signed-off-by: NGao Feng <gfree.wind@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>