wifi: iwlwifi: mvm: fix driver-set TX rates on old devices

In the Linux kernel, the following vulnerability has been resolved: wifi: iwlwifi: mvm: fix driver-set TX rates on old devices On old devices such as 7265D, rates are still encoded in version 1 format, which doesn't use the CCK/OFDM rate index (0-3/0-7) but rather their PLCP value (e.g. 10 for 1 Mbps CCK rate.) While introducing v3 rates, I changed the driver from internally handling v1 rates and converting to v2, to internally handling v3 and converting to v1 or v2 according to the firmware. I accordingly changed the code in iwl_mvm_mac80211_idx_to_hwrate() to no longer have different values for different APIs. This was correct. However, I later reverted this part of the change, because it was reported that I had broken beacon rates, causing a FW assert/crash. This caused TX_CMD rates to be set incorrectly, potentially causing a warning when reported back from the device as having been used. Fix this (hopefully correctly now) by handling beacon rates in the TX_CMD that's embedded in the beacon template command separately. Restore iwl_mvm_mac80211_idx_to_hwrate() to return only the rate index, not PLCP value, fixing the real TX_CMD.