net: Add a xfrm validate function to validate_xmit_skb

When we do IPsec offloading, we need a fallback for
packets that were targeted to be IPsec offloaded but
rerouted to a device that does not support IPsec offload.
For that we add a function that checks the offloading
features of the sending device and and flags the
requirement of a fallback before it calls the IPsec
output function. The IPsec output function adds the IPsec
trailer and does encryption if needed.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 17603bf..6793a30c 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1862,6 +1862,7 @@
 
 #ifdef CONFIG_XFRM_OFFLOAD
 void __net_init xfrm_dev_init(void);
+int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features);
 int xfrm_dev_state_add(struct net *net, struct xfrm_state *x,
 		       struct xfrm_user_offload *xuo);
 bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x);
@@ -1890,6 +1891,11 @@
 {
 }
 
+static inline int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features)
+{
+	return 0;
+}
+
 static inline int xfrm_dev_state_add(struct net *net, struct xfrm_state *x, struct xfrm_user_offload *xuo)
 {
 	return 0;