Refactor dladm crate

[daniel-levin]

This is a large, but self-contained change that
fixes up a few things in the dladm crate. In the
future I have Big Plans for running Bayesian
optimization loops on various link parameters,
and will need to use this crate. While this change is merely preparatory, I decided to fix some
things along the way.

First, dladm_handle_t is changed to no longer use the empty enum as an FFI type, which is unsound.
See: https://doc.rust-lang.org/nomicon/ffi.html

The crate no longer shells out to dladm.
It struck me as a bit gross to shell out to dladm
when we're linking against libdladm in the first place.

I renamed Handle to Dladm and called its most imporant method describe. In addition, some fields that
dladm furnishes us with anyway (upon calling
dladm_name2info) have been added to LinkInfo and
exported for use in Propolis.

Several disabled unit tests are added, which are useful for hacking on this crate.

Finally, I made it clear that this crate does no allocations. It's just one less thing to think about when reasoning about code linked into our VMM.

[github-actions]

license-eye has checked 385 files.

Valid	Invalid	Ignored	Fixed
293	1	91	0

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• crates/dladm/tests/dladm.rs

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docker run -it --rm -v $(pwd):/github/workspace apache/skywalking-eyes header fix

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