- Add libbpf as a submodule. This prevents having to plumb its location
around (which can't be passed to Cargo build scripts) and also
controls the version against which codegen has run.
- Move bpf written in C to the integration-test crate and define
constants for each probe.
- Remove magic; each C source file must be directly enumerated in the
build script and in lib.rs.
Replace all `assert!(matches!(..))` with `assert_matches!(..)`.
Remove the now-unused build-integration-test xtask command whose logic
doesn't match that of the build-and-run command.
This doesn't add any value; use `cargo build --tests` with
`--message-format=json` instead; parse the output using `cargo_metadata`
to discover the location of the test binary.
Move test/integration-test/src/tests -> test/integration-test/tests to
conform to
https://doc.rust-lang.org/book/ch11-03-test-organization.html#integration-tests.