flow_offload: restrict driver to pass one allowed bit to flow_action_hw_stats_types_check()

The intention of this helper was to allow driver to specify one type
that it supports, so not only "any" value would pass. So make the API
more strict and allow driver to pass only 1 bit that is going
to be checked.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>