Some (all?) management frames are incorrectly reported to mac80211 as
decrypted when actually the hardware did not decrypt them. This results
in speeds 3-5 times lower than expected, 20-30 Mbps instead of 100
Mbps.

Fix this by checking the encryption type field of the RX descriptor.
rtw88 does the same thing.

This fix was tested only with rtl8192du, which will use the same code.

Cc: stable@vger.kernel.org
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/4d600435-f0ea-46b0-bdb4-e60f173da8dd@gmail.com