[bug] TCP tunnel breaks after every request

==============Server side, firewall only open TCP 4001=========
$ ipfs version
ipfs version 0.4.15

$ ipfs id
"ID": [my vps ipfs id]
$ ipfs p2p listener open p2p-test /ip4/127.0.0.1/tcp/8081
{"Address":"/ip4/127.0.0.1/tcp/8081","Protocol":"/p2p/p2p-test"}

$ curl --socks5 127.0.0.1:8081 http://myip.ipip.net
IP：[my vps wan ip] amazon.com

==================Client side, symmetric NAT===========
$ ipfs version
ipfs version 0.4.15

$ ipfs p2p stream dial [my vps ipfs id] p2p-test /ip4/127.0.0.1/tcp/10102
{"Address":"/ip4/127.0.0.1/tcp/10102","Protocol":"/p2p/p2p-test"}

$ ipfs p2p stream dial [my vps ipfs id] p2p-test /ip4/127.0.0.1/tcp/10102
Error: listen tcp4 127.0.0.1:10102: bind: address already in use

$ curl --socks5 127.0.0.1:10102 http://myip.ipip.net
IP：[my vps wan ip] amazon.com

$ curl --socks5 127.0.0.1:10102 http://myip.ipip.net
curl: (7) Failed to connect to 127.0.0.1 port 10102: Connection refused

$ ipfs p2p stream dial [my vps ipfs id] p2p-test /ip4/127.0.0.1/tcp/10102
{"Address":"/ip4/127.0.0.1/tcp/10102","Protocol":"/p2p/p2p-test"}

$ curl --socks5 127.0.0.1:10102 http://myip.ipip.net
IP：[my vps wan ip] amazon.com

$ curl --socks5 127.0.0.1:10102 http://myip.ipip.net
curl: (7) Failed to connect to 127.0.0.1 port 10102: Connection refused

$ ipfs p2p stream dial [my vps ipfs id] p2p-test /ip4/127.0.0.1/tcp/10102
{"Address":"/ip4/127.0.0.1/tcp/10102","Protocol":"/p2p/p2p-test"}

$ curl --socks5 127.0.0.1:10102 http://myip.ipip.net
IP：[my vps wan ip] amazon.com

$ curl --socks5 127.0.0.1:10102 http://myip.ipip.net
curl: (7) Failed to connect to 127.0.0.1 port 10102: Connection refused

....

What a pity, TCP tunnel breaks after every request.

https://github.com/ipfs/go-ipfs/issues/3397#issuecomment-309306293

Start with the `ipfs p2p stream dial` and `curl --socks5` entry points shown in the report, reproducing the sequential-request failure on version 0.4.15. Trace why the local TCP listener is refused after the first request; done means the same tunnel accepts repeated requests without requiring another dial.

Written by the indexing model from the issue text.