mac80211: ignore NullFunc frames in the duplicate detection

NullFunc packets should never be duplicate just like
QoS-NullFunc packets.

We saw a client that enters / exits power save with
NullFunc frames (and not with QoS-NullFunc) despite the
fact that the association supports HT.
This specific client also re-uses a non-zero sequence number
for different NullFunc frames.
At some point, the client had to send a retransmission of
the NullFunc frame and we dropped it, leading to a
misalignment in the power save state.
Fix this by never consider a NullFunc frame as duplicate,
just like we do for QoS NullFunc frames.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=201449

CC: <stable@vger.kernel.org>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -1403,6 +1403,7 @@ ieee80211_rx_h_check_dup(struct ieee80211_rx_data *rx)
 		return RX_CONTINUE;
 
 	if (ieee80211_is_ctl(hdr->frame_control) ||
+	    ieee80211_is_nullfunc(hdr->frame_control) ||
 	    ieee80211_is_qos_nullfunc(hdr->frame_control) ||
 	    is_multicast_ether_addr(hdr->addr1))
 		return RX_CONTINUE;