nfp: flower-ct: implement action_merge check

Fill in code stub to check that the flow actions are valid for
merge. The actions of the flow X should not conflict with the
matches of flow X+1. For now this check is quite strict and
set_actions are very limited, will need to update this when
NAT support is added.

Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>