Slightly changed the interface sock_addr_remote - since we already
have a `__wasi_addr_t` structure which is an union, there's no need
for passing length around - the address buffer will always have the
right length (i.e. max of all address families).
Refer to [Networking API design](https://github.com/WebAssembly/WASI/issues/370)
and [feat(socket): berkeley socket API v2](https://github.com/WebAssembly/WASI/pull/459):
- Support the socket API of synchronous mode, including `socket/bind/listen/accept/send/recv/close/shutdown`,
the asynchronous mode isn't supported yet.
- Support adding `--addr-pool=<pool1,pool2,..>` argument for command line to identify the valid ip address range
- Add socket-api sample and update the document
