wifi: iwlwifi: mvm: validate TX_CMD response layout

wifi: iwlwifi: mvm: validate TX_CMD response layout

TX_CMD parsing uses frame_count to walk status entries and then
read the trailing SCD SSN. Make the minimum-length check follow
that exact runtime layout calculation before parsing the payload.

For new TX API, reject TX_CMD responses with frame_count != 1 and
warn/return in the aggregation handler to document that aggregated
accounting is expected via BA notifications.

Assisted-by: GitHubCopilot:gpt-5.3-codex
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260715215523.0474ee89bab9.I84f151aabecb8921b587da092f29f78c47128f0f@changeid