Add options to WasiCtx for toggling TCP and UDP on and off

[rylev]

This adds options to WasiCtx that allow disabling TCP and UDP wholesale. For TCP this prevents usage of binding, connecting, listening, and accepting while for UDP it prevents binding.

[alexcrichton]

Thanks! Mind adding a test for this as well?

If you're up for it too it'd be nice to get this hooked up to -S/--wasi options on the CLI, for example -S tcp would enable TCP connections while -S udp would enable UDP. (similarly -S tcp=n would disable TCP.

[rylev]

@alexcrichton I've addressed your feedback for everything but the test. Looking at the testing structure in wasmtime, I couldn't find a place where a test for this should clearly go. For example, I don't see a place where name lookups not being allowed is being tested. Any pointers on where to test this would be most appreciated.

[alexcrichton]

Ah yes that's a good point that name lookups not being allowed isn't tested right now. Since that was added it'd become easier to add tests though so I think the best way to test this would be something along the lines of a cli_* tests in crates/test-programs/src/bin/*.rs and then a corresponding test function in this module. You could then pass -S ... flags to disable/enable the network and/or validate it's enabled/disabled by default.

Alternatively a preview2_* test could be added and this function could be modified to look at the name and configure disallowing options based on that.

[rylev]

@alexcrichton I added a test for TCP - I will add a test in #7648 for UDP since those tests would fail without the fixes there.

[vicspina]

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