net: bridge: fix build when setting skb->offload_fwd_mark with CONFIG_NET_SWITCHDEV=n

Switchdev support can be disabled at compile time, and in that case,
struct sk_buff will not contain the offload_fwd_mark field.

To make the code in br_forward.c work in both cases, we do what is done
in other places and we create a helper function, with an empty shim
definition, that is implemented by the br_switchdev.o translation module.
This is always compiled if and only if CONFIG_NET_SWITCHDEV is y or m.
Reported-by: kernel test robot <lkp@intel.com>
Fixes: 47211192 ("net: bridge: switchdev: allow the TX data plane forwarding to be offloaded")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_forward.c

@@ -48,7 +48,7 @@ int br_dev_queue_push_xmit(struct net *net, struct sock *sk, struct sk_buff *skb
 		skb_set_network_header(skb, depth);
 	}
 
-	skb->offload_fwd_mark = br_switchdev_frame_uses_tx_fwd_offload(skb);
+	br_switchdev_frame_set_offload_fwd_mark(skb);
 
 	dev_queue_xmit(skb);
 

net/bridge/br_private.h

@@ -1881,6 +1881,8 @@ static inline void br_sysfs_delbr(struct net_device *dev) { return; }
 #ifdef CONFIG_NET_SWITCHDEV
 bool br_switchdev_frame_uses_tx_fwd_offload(struct sk_buff *skb);
 
+void br_switchdev_frame_set_offload_fwd_mark(struct sk_buff *skb);
+
 void nbp_switchdev_frame_mark_tx_fwd_offload(const struct net_bridge_port *p,
 					     struct sk_buff *skb);
 void nbp_switchdev_frame_mark_tx_fwd_to_hwdom(const struct net_bridge_port *p,
@@ -1910,6 +1912,10 @@ static inline bool br_switchdev_frame_uses_tx_fwd_offload(struct sk_buff *skb)
 	return false;
 }
 
+static inline void br_switchdev_frame_set_offload_fwd_mark(struct sk_buff *skb)
+{
+}
+
 static inline void
 nbp_switchdev_frame_mark_tx_fwd_offload(const struct net_bridge_port *p,
 					struct sk_buff *skb)

net/bridge/br_switchdev.c

@@ -28,6 +28,11 @@ bool br_switchdev_frame_uses_tx_fwd_offload(struct sk_buff *skb)
 	return BR_INPUT_SKB_CB(skb)->tx_fwd_offload;
 }
 
+void br_switchdev_frame_set_offload_fwd_mark(struct sk_buff *skb)
+{
+	skb->offload_fwd_mark = br_switchdev_frame_uses_tx_fwd_offload(skb);
+}
+
 /* Mark the frame for TX forwarding offload if this egress port supports it */
 void nbp_switchdev_frame_mark_tx_fwd_offload(const struct net_bridge_port *p,
 					     struct sk_buff *skb)