mlxsw: acl: Add ip ttl acl element

Define new element for ip ttl and place it into scratch area.

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