iwlwifi: add TGN flag to qos parameters

This patch adds TGN flag to QoS parameters. This flag governs enablement of
NAV shortening with CF-End and filters in 4 or 8K RX AMSDU packets

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>