iwlwifi: mvm: improve latency when there is a reorder timeout

When there is a reorder timeout, we may get to a situation
where we have the timeout latency for all the next 64 frames.
This happens since NSSN is behind for a while, and the driver
won't release the frames, since it is not allowed by NSSN.
As a result the frame is stored in the reorder buffer although
there is no hole, and released 100 ms later.
Add a direct comparison to the reorder buffer head, and release
immediately if possible.

For example:
Frame 0 is missed. We receive frame 1, and store it in the buffer.
After 100 ms, frame 1 is released and reorder buffer head is 2.
We then receive frame 2, with NSSN 0, and store it instead of
releasing it.
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c

@@ -719,6 +719,22 @@ static bool iwl_mvm_reorder(struct iwl_mvm *mvm,
 		return false;
 	}
 
+	/*
+	 * release immediately if there are no stored frames, and the sn is
+	 * equal to the head.
+	 * This can happen due to reorder timer, where NSSN is behind head_sn.
+	 * When we released everything, and we got the next frame in the
+	 * sequence, according to the NSSN we can't release immediately,
+	 * while technically there is no hole and we can move forward.
+	 */
+	if (!buffer->num_stored && sn == buffer->head_sn) {
+		if (!amsdu || last_subframe)
+			buffer->head_sn = ieee80211_sn_inc(buffer->head_sn);
+		/* No need to update AMSDU last SN - we are moving the head */
+		spin_unlock_bh(&buffer->lock);
+		return false;
+	}
+
 	index = sn % buffer->buf_size;
 
 	/*