emulators/xen-kernel: improve package message
Use onifconsole for the Xen console, so that when booting bare metal
there are no annoying messages about a console being off. Also note
the usage of vm.max_user_wired instead of vm.max_wired on FreeBSD >
- Finally expand a little bit on how to get a working serial and VGA
consoles simultaneously.
Sponsored by: Citrix Systems R&D
Approved by: bapt (implicit)