[COMPLIANCE] Add Copyright and License Headers

[hashicorp-copywrite]

Hi there 👋

This PR was auto-generated as part of an internal review of public repositories that are not in compliance with HashiCorp's licensing standards.

Frequently Asked Questions

Why am I getting this PR?

This pull request was created because one or more source code files were found missing copyright and/or license headers.

More info is available in the RFC

How do you determine which files should get copyright headers?

Attempts are made to skip scanning autogenerated files (e.g., `go.mod`) and prose. If you find file types you feel should be excluded from future scans, please reach out to:

#proj-software-copyright

I have a file or folder which should be exempted, how do I do that?

You may exempt certain files or folders from being scanned by adding a `.copywrite.hcl` config in the root of your repo. You can use the [`copywrite init`](https://go.hashi.co/copywrite) command to interactively create a config for this project.

An example schema can be found below. Add a doublestar**-capable pattern to the header_ignore list to skip it in future scans.

# (OPTIONAL) Overrides the copywrite config schema version
# Default: 1
schema_version = 1

project {
  # (OPTIONAL) SPDX-compatible license identifier
  # Leave blank if you don't wish to license the project
  # Default: "MPL-2.0"
  # license = ""

  # (OPTIONAL) Represents the year that the project initially began
  # Default: <the year the repo was first created>
  # copyright_year = 0

  # (OPTIONAL) A list of globs that should not have copyright or license headers .
  # Supports doublestar glob patterns for more flexibility in defining which
  # files or folders should be ignored
  # Default: []
  header_ignore = [
    # "vendor/**",
    # "**autogen**",
  ]
}

More information about configuration options is available in [the documentation](https://github.com/hashicorp/copywrite#config-structure).

I added a config. How do I trigger this PR to be rebased?

HashiCorp employees can use the [Copywrite SlackBot](https://hashicorp.slack.com/archives/D052WARFFS8) to trigger a rebase. You can DM the slackbot with "headers go-sockaddr" to trigger a PR rebasing.

Why don't the headers include a copyright date?

Copyright headers are not required to include a year. In the interest of pragmatism, HashiCorp has decided to exclude the year from headers and instead list it in the LICENSE file at the root of the repository instead.

Additional FAQs are available at https://go.hashi.co/header-faq

Please approve and merge this PR in a timely manner to keep this source code compliant with our OSS license agreement. If you have any questions or feedback, reach out to #proj-software-copyright.

Thank you!

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Powered by copywrite, made with ❤️ by @hashicorp

[schmichael]

f7bc6c4 adds copyright headers to third party code in the cmd/sockaddr/vendor directory. We need to either remove that, or preferably, switch from vendoring to go.mod.