nfp: flower: add ipv6 set flow label and hop limit offload

Add ipv6 set flow label and hop limit action offload. Since pedit sets
headers per 4 byte word, we need to ensure that setting either version,
priority, payload_len or nexthdr does not get offloaded.

Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>