nfp: add whitelist of supported flow dissector

Previously we did not check the flow dissector against a list of allowed
and supported flow key dissectors. This patch introduces such a list and
correctly rejects unsupported flow keys.

Fixes: 43f84b72 ("nfp: add metadata to each flow offload")
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>