In socks5_connect:

In socks5_connect:
- make the buffers quite a bit smaller.
- properly report "socks5 server unreachable" failures.
- let strncpy() use the whole buffer. Using a length of 0xffu wasn't actually
  wrong, but requires too much thinking as it doesn't depend on the buffer size.
- log a message if the socks5 server sends more data than expected.
- add some assertions and comments.