fix(s2n-quic-xdp): correct tokio feature dependency

[jmayclin]

Description of changes:

We are currently unable to publish to crates.io because s2n-quic-xdp can't be published. This is because s2n-quic-xdp depends on the net feature, but we forgot to specify that in the Cargo.toml.

Previously the s2n-quic-xdp crate was using the default feature resolver, which unified features across normal and dev dependencies, so the build pulled in full tokio features because tokio-full is a dev dependency.

Publishing crates uses a different feature resolver that doesn't pull in dev-dependencies, so the build failed because our build had a dependency on the net feature of tokio that wasn't fully modeled in the Cargo.toml

This PR

• adds explicity dependency on the tokio net feature.
• adds the s2n-quic-xdp crate to the package build check
• switches the tools workspace to use the non-unifying feature resolver (so this failure mode is now covered by CI)

Edit: The section previously talked about how it would be difficult to write a check for this with cargo publish --dry-run but the feature-resolver = 2 should allow us to correctly test for this failure in CI.

Testing:

This was verified with the following command

cargo package --manifest-path tools/xdp/s2n-quic-xdp/Cargo.toml

This failed before the change, and now succeeds.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[camshaft]

For that workflow we should probably be doing a cargo publish --dry-run to avoid any workspace-specific configuration. The trick is, like you mention, is when we bump the version and it can't resolve our deps.

[jmayclin]

Here are some issues with context

rust-lang/cargo#1796