net: flow: Add l3mdev flow update

Add l3mdev hook to set FLOWI_FLAG_SKIP_NH_OIF flag and update oif/iif
in flow struct if its oif or iif points to a device enslaved to an L3
Master device. Only 1 needs to be converted to match the l3mdev FIB
rule. This moves the flow adjustment for l3mdev to a single point
catching all lookups. It is redundant for existing hooks (those are
removed in later patches) but is needed for missed lookups such as
PMTU updates.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/l3mdev.h b/include/net/l3mdev.h
index e900950..81e175e 100644
--- a/include/net/l3mdev.h
+++ b/include/net/l3mdev.h
@@ -49,6 +49,8 @@
 int l3mdev_fib_rule_match(struct net *net, struct flowi *fl,
 			  struct fib_lookup_arg *arg);
 
+void l3mdev_update_flow(struct net *net, struct flowi *fl);
+
 int l3mdev_master_ifindex_rcu(const struct net_device *dev);
 static inline int l3mdev_master_ifindex(struct net_device *dev)
 {
@@ -290,6 +292,10 @@
 {
 	return 1;
 }
+static inline
+void l3mdev_update_flow(struct net *net, struct flowi *fl)
+{
+}
 #endif
 
 #endif /* _NET_L3MDEV_H_ */