wasi: unnecessarily strong assumptions about fd 0-2

[yamt]

because the plain wasip1 dosen't have connect/listen,
sometimes embedders play a trick to pass an already connected/listening socket.

eg. https://github.com/yamt/garbage/tree/master/wasm/httpd

unfortunately these tricks don't work well for the current wamr if the embedder uses fd 0-2 for it
(as the above example does by default)
because it has unnecessarily strong assumptions about how fd 0-2 are used.

[lum1n0us]

sometimes embedders play a trick to pass an already connected/listening socket.

Please kindly highlight those lines.

[yamt]

sometimes embedders play a trick to pass an already connected/listening socket.

Please kindly highlight those lines.

https://github.com/yamt/garbage/blob/4478d1d09d556347062ea6c9b1d161a93775b55e/wasm/httpd/test.sh#L10
https://github.com/yamt/garbage/blob/4478d1d09d556347062ea6c9b1d161a93775b55e/listenexec/main.c#L120