Test result without patch on comment #1:
11n:
------------------------------------------------------------
Client connecting to 192.168.158.106, TCP port 5001
TCP window size: 416 KByte (WARNING: requested 100 MByte)
------------------------------------------------------------
[ 3] local 192.168.158.107 port 36578 connected with 192.168.158.106 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 24.0 MBytes 20.1 Mbits/sec
[ 3] 10.0-20.0 sec 23.5 MBytes 19.7 Mbits/sec
[ 3] 20.0-30.0 sec 23.8 MBytes 19.9 Mbits/sec
[ 3] 30.0-40.0 sec 22.9 MBytes 19.2 Mbits/sec
[ 3] 40.0-50.0 sec 24.1 MBytes 20.2 Mbits/sec
[ 3] 50.0-60.0 sec 24.0 MBytes 20.1 Mbits/sec
[ 3] 60.0-70.0 sec 19.2 MBytes 16.1 Mbits/sec
[ 3] 70.0-80.0 sec 16.0 MBytes 13.4 Mbits/sec
[ 3] 80.0-90.0 sec 23.8 MBytes 19.9 Mbits/sec
[ 3] 90.0-100.0 sec 23.2 MBytes 19.5 Mbits/sec
[ 3] 100.0-110.0 sec 23.1 MBytes 19.4 Mbits/sec
[ 3] 110.0-120.0 sec 23.4 MBytes 19.6 Mbits/sec
[ 3] 0.0-120.1 sec 271 MBytes 18.9 Mbits/sec

11AC:
------------------------------------------------------------
Client connecting to 192.168.158.106, TCP port 5001
TCP window size: 416 KByte (WARNING: requested 100 MByte)
------------------------------------------------------------
[ 3] local 192.168.158.107 port 36594 connected with 192.168.158.106 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 12.0 MBytes 10.1 Mbits/sec
[ 3] 10.0-20.0 sec 12.1 MBytes 10.2 Mbits/sec
[ 3] 20.0-30.0 sec 12.6 MBytes 10.6 Mbits/sec
[ 3] 30.0-40.0 sec 12.8 MBytes 10.7 Mbits/sec
[ 3] 40.0-50.0 sec 9.12 MBytes 7.65 Mbits/sec
[ 3] 50.0-60.0 sec 11.8 MBytes 9.86 Mbits/sec
[ 3] 60.0-70.0 sec 12.2 MBytes 10.3 Mbits/sec
[ 3] 70.0-80.0 sec 11.1 MBytes 9.33 Mbits/sec
[ 3] 80.0-90.0 sec 11.8 MBytes 9.86 Mbits/sec
[ 3] 90.0-100.0 sec 11.5 MBytes 9.65 Mbits/sec
[ 3] 100.0-110.0 sec 11.6 MBytes 9.75 Mbits/sec
[ 3] 110.0-120.0 sec 12.5 MBytes 10.5 Mbits/sec
[ 3] 0.0-120.2 sec 141 MBytes 9.86 Mbits/sec

Test result with the patch on comment #1:
11n:
------------------------------------------------------------
Client connecting to 192.168.158.106, TCP port 5001
TCP window size: 416 KByte (WARNING: requested 100 MByte)
------------------------------------------------------------
[ 3] local 192.168.158.107 port 57252 connected with 192.168.158.106 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 172 MBytes 144 Mbits/sec
[ 3] 10.0-20.0 sec 184 MBytes 154 Mbits/sec
[ 3] 20.0-30.0 sec 100 MBytes 84.3 Mbits/sec
[ 3] 30.0-40.0 sec 172 MBytes 144 Mbits/sec
[ 3] 40.0-50.0 sec 187 MBytes 157 Mbits/sec
[ 3] 50.0-60.0 sec 180 MBytes 151 Mbits/sec
[ 3] 60.0-70.0 sec 177 MBytes 148 Mbits/sec
[ 3] 70.0-80.0 sec 190 MBytes 159 Mbits/sec
[ 3] 80.0-90.0 sec 179 MBytes 150 Mbits/sec
[ 3] 90.0-100.0 sec 183 MBytes 153 Mbits/sec
[ 3] 100.0-110.0 sec 180 MBytes 151 Mbits/sec
[ 3] 110.0-120.0 sec 185 MBytes 155 Mbits/sec
[ 3] 0.0-120.0 sec 2.04 GBytes 146 Mbits/sec

11AC:
------------------------------------------------------------
Client connecting to 192.168.158.106, TCP port 5001
TCP window size: 416 KByte (WARNING: requested 100 MByte)
------------------------------------------------------------
[ 3] local 192.168.158.107 port 57236 connected with 192.168.158.106 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 102 MBytes 85.5 Mbits/sec
[ 3] 10.0-20.0 sec 79.0 MBytes 66.3 Mbits/sec
[ 3] 20.0-30.0 sec 96.0 MBytes 80.5 Mbits/sec
[ 3] 30.0-40.0 sec 103 MBytes 86.3 Mbits/sec
[ 3] 40.0-50.0 sec 99.0 MBytes 83.0 Mbits/sec
[ 3] 50.0-60.0 sec 93.8 MBytes 78.6 Mbits/sec
[ 3] 60.0-70.0 sec 93.1 MBytes 78.1 Mbits/sec
[ 3] 70.0-80.0 sec 104 MBytes 87.5 Mbits/sec
[ 3] 80.0-90.0 sec 107 MBytes 89.9 Mbits/sec
[ 3] 90.0-100.0 sec 107 MBytes 89.7 Mbits/sec
[ 3] 100.0-110.0 sec 106 MBytes 89.3 Mbits/sec
[ 3] 110.0-120.0 sec 106 MBytes 88.7 Mbits/sec
[ 3] 0.0-120.0 sec 1.17 GBytes 83.6 Mbits/sec

Test comment on client side:
u@u-XPS-13-9360:~$ iperf -c serverip -w 100M -t 120 -i 10