net: add netif_is_geneve()

Add a helper function to determine if the type of a netdev is geneve based
on its rtnl_link_ops. This allows drivers that may wish to offload tunnels
to check the underlying type of the device.

A recent patch added a similar helper to vxlan.h

Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/geneve.h

@@ -60,6 +60,12 @@ struct genevehdr {
 	struct geneve_opt options[];
 };
 
+static inline bool netif_is_geneve(const struct net_device *dev)
+{
+	return dev->rtnl_link_ops &&
+	       !strcmp(dev->rtnl_link_ops->kind, "geneve");
+}
+
 #ifdef CONFIG_INET
 struct net_device *geneve_dev_create_fb(struct net *net, const char *name,
 					u8 name_assign_type, u16 dst_port);