ath10k: handle attention flags correctly when using A-MSDU

In case of A-MSDU RX we should check attention flags
correctly to be sure we report correct FCS status for
A-MSDU subframes. Without a patch we could report A-MSDU
subframes with wrong FCS as a correct to the stack, next
get a lot of DUP ACK TCP packets. Finally TP drop is seen
and this drop depends on FCS errors ratio for A-MSDU frame.

Example test case when TP drop is seen:
- ath10k configured as an AP
- used ath10k station
- forced A-MSDU (7 frames) on STA
- other traffic on channel (often FCS errors)
- monitor iface added on AP
- TCP STA -> AP traffic (iperf)

a) Iperf logs for case without the patch:

echo "1 64" > htt_max_amsdu_ampdu // disable A-MSDU
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 5.0 sec  56.6 MBytes  95.0 Mbits/sec
[  3]  5.0-10.0 sec  60.4 MBytes   101 Mbits/sec
[  3] 10.0-15.0 sec  60.2 MBytes   101 Mbits/sec
[  3] 15.0-20.0 sec  60.2 MBytes   101 Mbits/sec
[  3] 20.0-25.0 sec  63.8 MBytes   107 Mbits/sec
[  3] 25.0-30.0 sec  64.9 MBytes   109 Mbits/sec

echo "7 64" > htt_max_amsdu_ampdu  // set 7 A-MSDU subframes
[  3] 30.0-35.0 sec  40.0 MBytes  67.1 Mbits/sec
[  3] 35.0-40.0 sec  35.9 MBytes  60.2 Mbits/sec
[  3] 40.0-45.0 sec  36.9 MBytes  61.9 Mbits/sec
[  3] 45.0-50.0 sec  37.9 MBytes  63.5 Mbits/sec
[  3] 50.0-55.0 sec  34.5 MBytes  57.9 Mbits/sec
[  3] 55.0-60.0 sec  25.4 MBytes  42.6 Mbits/sec
[  3] 60.0-65.0 sec  48.2 MBytes  81.0 Mbits/sec
[  3] 65.0-70.0 sec  28.8 MBytes  48.2 Mbits/sec
[  3] 70.0-75.0 sec  29.2 MBytes  49.1 Mbits/sec
[  3] 75.0-80.0 sec  22.9 MBytes  38.4 Mbits/sec
[  3] 80.0-85.0 sec  26.4 MBytes  44.2 Mbits/sec
[  3] 85.0-90.0 sec  31.5 MBytes  52.8 Mbits/sec

b) Iperf logs for case with patch:

echo "1 64" > htt_max_amsdu_ampdu // disable A-MSDU
[  3] local 192.168.12.2 port 57512 connected with 192.168.12.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 5.0 sec  60.8 MBytes   102 Mbits/sec
[  3]  5.0-10.0 sec  62.2 MBytes   104 Mbits/sec
[  3] 10.0-15.0 sec  60.9 MBytes   102 Mbits/sec

echo "7 64" > htt_max_amsdu_ampdu  // set 7 A-MSDU subframes
[  3] 15.0-20.0 sec  68.1 MBytes   114 Mbits/sec
[  3] 20.0-25.0 sec  80.5 MBytes   135 Mbits/sec
[  3] 25.0-30.0 sec  83.0 MBytes   139 Mbits/sec
[  3] 30.0-35.0 sec  79.1 MBytes   133 Mbits/sec
[  3] 35.0-40.0 sec  77.1 MBytes   129 Mbits/sec
[  3] 40.0-45.0 sec  77.4 MBytes   130 Mbits/sec

Reported-by: Denton Gentry <denton.gentry@gmail.com>
Signed-off-by: Janusz Dziedzic <janusz.dziedzic@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Merge branch 'ath-next' into ath-qca