fix(socks5): should not dial returned bind addr directly

[mzz2017]

When server returns an any ip (0.0.0.0 or [::]), we should use conventional ip to replace the any ip given (0.0.0.0 or [::]). This behaviour adapts to most situations.

See v2fly/v2ray-core#523

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Problem happens when socks5 proxy works on remote servers and different implementation will given different bind addr.

For most situations it is issues of servers. However, clients should behave normally in one case that returned bind addr is an ANYIP (0.0.0.0 or [::]), which indicate that we should use a conventional remote address to connect.

RFC does not illustrate the mechanism of bind addr; it is based on experience.

[mzz2017]

My remote server is 10.xxx.xxx.xxx with refined v2ray-core by PR#523 mentioned above and socks5 port 20170 on.

Current version(0.13.0):

2020/12/16 16:03:43 group.go:182: [group] only 1 forwarder found, disable health checking
2020/12/16 16:03:43 server.go:105: [socks5] listening UDP on :1080
2020/12/16 16:03:43 mixed.go:68: [mixed] listening TCP on :1080
2020/12/16 16:03:45 server.go:142: [socks5u] 127.0.0.1:41632 <-> 223.5.5.5:53 via 10.xxx.xxx.xxx:20170
2020/12/16 16:03:45 server.go:150: [socks5u] remote write error: write udp [::]:57461->0.0.0.0:20170: sendto: cannot assign requested address

After the fix by #212:

2020/12/16 16:04:56 group.go:182: [group] only 1 forwarder found, disable health checking
2020/12/16 16:04:56 mixed.go:68: [mixed] listening TCP on :1080
2020/12/16 16:04:56 server.go:105: [socks5] listening UDP on :1080
2020/12/16 16:04:58 server.go:142: [socks5u] 127.0.0.1:41778 <-> 223.5.5.5:53 via 10.xxx.xxx.xxx:20170

The server side socks5 implementation of glider is not perfect but just ok (behave like clash). So it is not included in this fix.