net: don't reforward packets already forwarded by offload device

Just before queuing skb for xmit on port, check if skb has been marked by
switchdev port driver as already fordwarded by device.  If so, drop skb.  A
non-zero skb->offload_fwd_mark field is set by the switchdev port
driver/device on ingress to indicate the skb has already been forwarded by
the device to egress ports with matching dev->skb_mark.  The switchdev port
driver would assign a non-zero dev->offload_skb_mark for each device port
netdev during registration, for example.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1456,6 +1456,8 @@ enum netdev_priv_flags {
  *
  *	@xps_maps:	XXX: need comments on this one
  *
+ *	@offload_fwd_mark:	Offload device fwding mark
+ *
  *	@trans_start:		Time (in jiffies) of last Tx
  *	@watchdog_timeo:	Represents the timeout that is used by
  *				the watchdog ( see dev_watchdog() )
@@ -1697,6 +1699,10 @@ struct net_device {
 	struct xps_dev_maps __rcu *xps_maps;
 #endif
 
+#ifdef CONFIG_NET_SWITCHDEV
+	u32			offload_fwd_mark;
+#endif
+
 	/* These may be needed for future network-power-down code. */
 
 	/*