Add command brctl

[leongross]

Add cmd/brctl which aims to be a (near) feature complete implementation of brctl.

TODOs

• Enhance test coverage
  • add vmtest
• minifiy str_to_jiffies
• getBridge interface parsing
• Setgcint command
• get interfaces from bridges
• improve documentation

[rminnich]

nice! This is going to be very useful.

[10000TB]

Do we have steps to validate traffic are transferred properly ?

[10000TB]

Edit: NVM -- discussed offline, I mis-understood the github UI. I was told this PR was opened from a fork of u-root.

---

@leongross Hi Leon, looks like this Draft is pushed against upstream u-root

leongross wants to merge 13 commits into u-root:main from leongross:cmds/brctl

Could you push against a fork of u-root, and make this as a PR ?

This looks like review-worthy.

[leongross]

@10000TB I'm not quite sure what kind of review process you suggest.
My PR goes from my private fork to the upstream u-root. What benefit is there to create a PR for another fork or even my own? There still needs to be a PR for upstream u-root after all, so why create another layer?
As I see it the procedure of this PR adheres to CONTRIBUTING.md guide. Maybe I misunderstood your suggestion, so I'd be glad if you could clarify.

[10000TB]

@10000TB I'm not quite sure what kind of review process you suggest. My PR goes from my private fork to the upstream u-root. What benefit is there to create a PR for another fork or even my own? There still needs to be a PR for upstream u-root after all, so why create another layer? As I see it the procedure of this PR adheres to CONTRIBUTING.md guide. Maybe I misunderstood your suggestion, so I'd be glad if you could clarify.

you good. I mis-understood the github UI ;)

[ChriMarMe]

Well, tests run or being skipped if eth0/eth1 are not present in setup. Dunno how to fix the coverage complains.

[10000TB]

Well, tests run or being skipped if eth0/eth1 are not present in setup. Dunno how to fix the coverage complains.

If you look at each file in this PR, there are alerts from "Codecov / codecov/patch" at each specific line telling you relevant lines are missing tests.

The codecov seems to suggest this PR brings down coverage by -38%. That is not acceptable :(

codecov/patch Failing after 1s — 34.50% of diff hit (target 57.32%)
[Details](https://github.com/u-root/u-root/pull/2971/checks?check_run_id=26115385569)
@codecov
codecov/patch/everything Failing after 1s — 34.50% of diff hit (target 56.45%)
[Details](https://github.com/u-root/u-root/pull/2971/checks?check_run_id=26115386655)
@codecov
codecov/project Failing after 1s — 56.85% (-0.47%) compared to 65d9fc3
[Details](https://github.com/u-root/u-root/pull/2971/checks?check_run_id=26115416946)
@codecov
codecov/project/cmds/exp — 30.54% (-38.96%) compared to 65d9fc3