wifi: iwlwifi: mvm/fw: Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

We have a flexible struct iwl_tx_cmd_v6 in the middle of a few structs,
but those don't even need the flexible part.

So, we add iwl_tx_cmd_v6_params, that will contain everything except the
flexible array and use this one for the containing structs.

Also, as part of the refactoring remove unused flex array `payload`.

So, with these changes, fix the following warnings:

drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tdls.h:134:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tdls.h:53:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tx.h:745:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mld/../fw/api/tx.h:764:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tdls.h:134:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tdls.h:53:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tx.h:745:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/iwlwifi/mvm/../fw/api/tx.h:764:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://msgid.link/aCUOQ6wdD1jQjO36@kspp


[use iwl_tx_cmd_v6_params as described in the changed commit message]
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250709224608.0785a61b0826.I6da02c2a12a5ed1e6d317045a6995d132850a455@changeid


Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>