nfp: flower: prepare for parameterisation of number of offload rules

The fixed number of offload flow rule is only supported scenario of one
ct zone, in the scenario of multiple ct zones, dynamic number and more
number of offload flow rules are required. In order to support scenario
of multiple ct zones, parameter num_rules is added for to offload flow
rules

Signed-off-by: Wentao Jia <wentao.jia@corigine.com>
Acked-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>