nfp: flower: offload tos and tunnel flags for ipv4 udp tunnels

Extract the tos and the tunnel flags from the tunnel key and offload these
action fields. Only the checksum and tunnel key flags are implemented in
fw so reject offloads of other flags. The tunnel key flag is always
considered set in the fw so enforce that it is set in the rule. Note that
the compulsory setting of the tunnel key flag and optional setting of
checksum is inline with how tc currently generates ipv4 udp tunnel
actions.

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