wifi: rtl8xxxu: Set IEEE80211_HW_SUPPORT_FAST_XMIT

According to commit 60d7900d ("wlcore: enable
IEEE80211_HW_SUPPORT_FAST_XMIT"), we can use this because all the chips
have hardware rate control.

This is one of the things mac80211 requires before it will handle MSDU
aggregation for us.
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/9b59e735-6b89-a557-fafc-2da87fdd5b48@gmail.com

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c

@@ -6998,6 +6998,7 @@ static int rtl8xxxu_probe(struct usb_interface *interface,
 	 * The firmware handles rate control
 	 */
 	ieee80211_hw_set(hw, HAS_RATE_CONTROL);
+	ieee80211_hw_set(hw, SUPPORT_FAST_XMIT);
 	ieee80211_hw_set(hw, AMPDU_AGGREGATION);
 
 	wiphy_ext_feature_set(hw->wiphy, NL80211_EXT_FEATURE_CQM_RSSI_LIST);