iwlwifi: mvm: rs: better match tx response rate to the LQ table

Currently rs uses the info in mac80211 tx status which is
a translation of the actual rate coming up from the FW in
the tx response. This is matched up against the LQ table first
rate to make sure this tx frame used the current LQ table.
Instead of using the translated mac80211 info it's easier and
cleaner to just pass the actual tx response rate in the driver
private data and use that for matching.
This becomes even more important once the FW begins to
decide on its own whether to use STBC/BFER/SISO.

Signed-off-by: Eyal Shapira <eyalx.shapira@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>