dpif: Factor 'type' and 'error' out of individual dpif_op members.

dpif: Factor 'type' and 'error' out of individual dpif_op members.

I'd like to change ->dpif_flow_put() and ->dpif_execute() in the dpif
provider to take the structures of the same names as parameters, instead of
passing them discrete parameters, because this seems like a more sensible
way to do things internally than to have two different ways to pass the
parameters.  It might even simplify code slightly.  But ->flow_put() and
->execute() wouldn't want the 'type' (because it's implied by the function
being called) or 'error' (because it would be the same as the return
value).  Although of course they could just ignore those members, it seems
slightly cleaner to omit them entirely, as this change allows.

Signed-off-by: Ben Pfaff <blp@nicira.com>