Misc cleanup. Remove support for FreeBSD < 12

[kev009]

@kostikbel I'd like to work on this driver with you and get it into the tree. This is my first pass at removing some unneeded code.

[kostikbel]

Generally, each change there, which is not a sincere bugfix, means the work for me when new vendor code drop is released. Unless you can convince Realtek to import our changes into their codebase, I am in fact leery to apply such cleanups.

At least we should try to keep bugfixes and cleanups separated. I did not thought how to organize the workflow to make it feasible. Might be there should be a branch on top of the 'my' branch, where 'my' only contains bug fixes, rebased.

[kev009]

@kostikbel ok let's do a second branch where we make these cleanups. I will split the cleanups out as you asked above. I am talking with RealTek now, they seem willing to work with us.

[kev009]

@kostikbel my desire is to merge this into src/main as re(9) since the in tree one is problematic. We will definitely want to coordinate with RealTek in any case.

I have a punch-list of things I'd like to do from reading the code many times. Maybe you can add to this anything else that would be necessary to get it into main?

• Use firmware(9) for mcu and phy patches
• Confirm with RealTek how they want to supply us mcu/phy patches
• Confirm with RealTek they will rebase on our driver or work with us in tree
• Add support for some PCI IDs that exist in re(4) in main right now.. dlink, tp-link, etc.
• Reintroduce debugnet support
• Reintroduce netmap support
• Run the code through a style(9) pass

I do not think these are necessary for main but would be nice stretch goals:

• Use iflib
• Add support for multiple tx/rx queues (depends on the above IMO)

[kostikbel]

What you have in those 4 commits looks fine to me.

I am unsure what to do next there. Do you want to keep the cleanup work on your fork/branch? Or do you prefer for me to accept the pull requests for it?

I created the 'reno' branch in my repo if you want PRs. Please create requests against this branch.