flow_dissector: Dissect tos and ttl from the tunnel info

Add dissection of the tos and ttl from the ip tunnel headers
fields in case a match is needed on them.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>