ip_tunnels: Add new flow flags field to ip_tunnel_key

This commit extends the ip_tunnel_key struct with a new field for the
flow flags, to pass them to the route lookups. This new field will be
populated and used in subsequent commits.

Signed-off-by: Paul Chaignon <paul@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/f8bfd4983bd06685a59b1e3ba76ca27496f51ef3.1658759380.git.paul@isovalent.com

include/net/ip_tunnels.h

@@ -54,6 +54,7 @@ struct ip_tunnel_key {
 	__be32			label;		/* Flow Label for IPv6 */
 	__be16			tp_src;
 	__be16			tp_dst;
+	__u8			flow_flags;
 };
 
 /* Flags for ip_tunnel_info mode. */