flow_dissector: dissect tunnel info

Move dissection of tunnel info from the flower classifier to the flow
dissector where all other dissection occurs.  This should not have any
behavioural affect on other users of the flow dissector.

Signed-off-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>