Rename ixgbe(4) to ix(4) and document sysctls

[kbowling]

Summary

This is related to PR 213026.

Before applying this patch, rename share/man/man4/ixgbe.4 to share/man/man4/ix.4.

[concussious.bugzilla_runbox.com]

This page is already mlinked to ix, which is I think correct, however the sysctls are a great addition if they're real (I don't have the HW). Can we get this section rebased into the current manpage? Kevin, does this look okay to you?

[kbowling]

In D32531#1078497, @concussious.bugzilla_runbox.com wrote:

This page is already mlinked to ix, which is I think correct, however the sysctls are a great addition if they're real (I don't have the HW). Can we get this section rebased into the current manpage? Kevin, does this look okay to you?

I think this change is actually correct and the mlink should be changed to go in the opposite direction.

The additional documentation looks ok, but these should be called "Loader Tunables" see em(4).

[concussious.bugzilla_runbox.com]

Since the author has not been seen in 3 years, and I wanted to work on this a bit too for some of my projects (improve apropos results, improve hardware release notes), I typed these up this as two commits in https://github.com/freebsd/freebsd-src/pull/1494 .

[kbowling]

Committed in the above PR