macvlan: forbid L2 fowarding offload for macvtap

L2 fowarding offload will bypass the rx handler of real device. This will make
the packet could not be forwarded to macvtap device. Another problem is the
dev_hard_start_xmit() called for macvtap does not have any synchronization.

Fix this by forbidding L2 forwarding for macvtap.

Cc: John Fastabend <john.r.fastabend@intel.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Acked-by: NJohn Fastabend <john.r.fastabend@intel.com.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/macvlan.c

@@ -338,6 +338,8 @@ static const struct header_ops macvlan_hard_header_ops = {
 	.cache_update	= eth_header_cache_update,
 };
 
+static struct rtnl_link_ops macvlan_link_ops;
+
 static int macvlan_open(struct net_device *dev)
 {
 	struct macvlan_dev *vlan = netdev_priv(dev);
@@ -353,7 +355,8 @@ static int macvlan_open(struct net_device *dev)
 		goto hash_add;
 	}
 
-	if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD) {
+	if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD &&
+	    dev->rtnl_link_ops == &macvlan_link_ops) {
 		vlan->fwd_priv =
 		      lowerdev->netdev_ops->ndo_dfwd_add_station(lowerdev, dev);