fix(tun): fixed performance degradation (#894)

Author: ibigbug

clash-netstack/examples/README.md

@@ -0,0 +1,22 @@
+```
+wtf@devbox-hypv:~/projects/clash-rs$ iperf3 -c dsm
+Connecting to host dsm, port 5201
+[  5] local 198.19.0.1 port 48868 connected to 10.0.0.11 port 5201
+[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
+[  5]   0.00-1.00   sec  66.5 MBytes   558 Mbits/sec    0    754 KBytes
+[  5]   1.00-2.00   sec  66.2 MBytes   556 Mbits/sec    0    754 KBytes
+[  5]   2.00-3.00   sec  63.8 MBytes   535 Mbits/sec    0    754 KBytes
+[  5]   3.00-4.00   sec  60.0 MBytes   503 Mbits/sec    0    754 KBytes
+[  5]   4.00-5.00   sec  63.8 MBytes   535 Mbits/sec    0    754 KBytes
+[  5]   5.00-6.00   sec  62.5 MBytes   524 Mbits/sec    0    754 KBytes
+[  5]   6.00-7.00   sec  63.8 MBytes   535 Mbits/sec    0    754 KBytes
+[  5]   7.00-8.00   sec  65.0 MBytes   545 Mbits/sec    0    754 KBytes
+[  5]   8.00-9.00   sec  61.2 MBytes   514 Mbits/sec    0    754 KBytes
+[  5]   9.00-10.00  sec  61.2 MBytes   514 Mbits/sec    0    754 KBytes
+- - - - - - - - - - - - - - - - - - - - - - - - -
+[ ID] Interval           Transfer     Bitrate         Retr
+[  5]   0.00-10.00  sec   634 MBytes   532 Mbits/sec    0             sender
+[  5]   0.00-10.01  sec   630 MBytes   528 Mbits/sec                  receiver
+
+iperf Done.
+```