iwlwifi: mvm: rs: fix and cleanup rs_get_rate_action

iwlwifi: mvm: rs: fix and cleanup rs_get_rate_action

commit e53839eb9882c99d3781eab0fe1b2d4369a6a2cc upstream.

Change the down/upscale decision logic a bit to be based
on different success ratio thresholds. This fixes the implementation
compared to the rate scale algorithm which was planned to yield
optimal results. Also fix a case where a lower rate wasn't explored
despite being a potential for better throughput.
While at it rewrite rs_get_rate_action to be more clear and clean.

Signed-off-by: Eyal Shapira <eyalx.shapira@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>