iwlwifi: mvm: Add support for new rate_n_flags in tx_cmd.

As part of the new rate_n_flags, tx_cmd API has changed.
Add support for these changes.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211017162352.26efa51624b1.Ic96ae4d81b3ff07fb514df2b5f6a8e470e4d3778@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>