rsi: Fix TX EAPOL packet handling against iwlwifi AP

In case RSI9116 SDIO WiFi operates in STA mode against Intel 9260 in AP mode,
the association fails. The former is using wpa_supplicant during association,
the later is set up using hostapd:

iwl$ cat hostapd.conf
interface=wlp1s0
ssid=test
country_code=DE
hw_mode=g
channel=1
wpa=2
wpa_passphrase=test
wpa_key_mgmt=WPA-PSK
iwl$ hostapd -d hostapd.conf

rsi$ wpa_supplicant -i wlan0 -c <(wpa_passphrase test test)

The problem is that the TX EAPOL data descriptor RSI_DESC_REQUIRE_CFM_TO_HOST
flag and extended descriptor EAPOL4_CONFIRM frame type are not set in case the
AP is iwlwifi, because in that case the TX EAPOL packet is 2 bytes shorter.

The downstream vendor driver has this change in place already [1], however
there is no explanation for it, neither is there any commit history from which
such explanation could be obtained.

[1] https://github.com/SiliconLabs/RS911X-nLink-OSD/blob/master/rsi/rsi_91x_hal.c#L238

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Angus Ainslie <angus@akkea.ca>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Martin Kepplinger <martink@posteo.de>
Cc: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Cc: Siva Rebbagondla <siva8118@gmail.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201015111616.429220-1-marex@denx.de

drivers/net/wireless/rsi/rsi_91x_hal.c

@@ -248,7 +248,8 @@ int rsi_prepare_data_desc(struct rsi_common *common, struct sk_buff *skb)
 			rsi_set_len_qno(&data_desc->len_qno,
 					(skb->len - FRAME_DESC_SZ),
 					RSI_WIFI_MGMT_Q);
-		if ((skb->len - header_size) == EAPOL4_PACKET_LEN) {
+		if (((skb->len - header_size) == EAPOL4_PACKET_LEN) ||
+		    ((skb->len - header_size) == EAPOL4_PACKET_LEN - 2)) {
 			data_desc->misc_flags |=
 				RSI_DESC_REQUIRE_CFM_TO_HOST;
 			xtend_desc->confirm_frame_type = EAPOL4_CONFIRM;