xen: miscellaneous fixes to the documentation

[royger]

Summary

Those include:

• Clarify which FreeBSD versions support Xen 4.7 (PVHv1) and Xen 4.11 or greater (PVHv2),
• Use onif for the Xen console.
• Add a rune to load if_tap at boot.
• Remove the restriction to use MMCFG PCI accesses for Xen >= 4.11.
• Make the mention of /var/log/xen a tip so it's more visible.
• Update the example guest creation to use FreeBSD 12.0 installer image.

[bcr]

Two suggestions, nothing major.

en_US.ISO8859-1/books/handbook/virtualization/chapter.xml

1512–1517

The <tip> needs to have an empty line above it and the <para> inside should be indented. Run textproc/igor over your changed file to get some useful reports on what to change.

1579

I need to dig into whether we can use the &latest; or &latest2; variables to automatically reflect the latest FreeBSD releases here. That way, we don't need to remember to bump this every time a new release comes out. For now, you could wrap that release number in <replaceable>s to indicate that something else could be put in that position.

[royger]

Thanks, all fixed :).

[royger]

Apply requested fixes, run igor.

[bcr]

Looks good. Can you commit that directly or should I take care of it?