Move Xen Kernel menuitem to Boot Options submenu.

[dteske]

Summary

Move Xen Kernel menuitem to Boot Options submenu. Prevent conflict with
upcoming Boot Environment menu. The Xen Kernel is dynamically appended
after the last menuitem in the Boot Options submenu. If xen_kernel is not
defined in loader.conf(5) the Xen Kernel menuitem displays "N/A" versus
"On"/"off". While here, fix-up the pkg-message (make capitalization of
"in" vs. "In" consistent; make use of trailing ":" consistent; move a
comment out of the way of file contents, etc.).

Test Plan

NB: Requires 11.0-CURRENT@r277215 or later.

1. Install emulators/xen-kernel
2. Do the prescribed steps in pkg-message
3. Reboot
4. If your system has VT-d CPUID capability, xen_kernel will be loaded and the machine will boot. sysctl kern.bootfile shows the Xen kernel otherwise the Xen kernel will kernel panic.
5. Reboot and this time go into the Boot Options submenu and toggle Xen Kernel to "off" and press Enter to boot. sysctl kern.bootfile shows the normal FreeBSD kernel.
6. If as-described above, the toggle is working as expected.

[dteske]

Oops; this is the working code

[allanjude]

Tested for the following cases:

default case: boots xen
o, x, 1, 1 (toggle xen off) boots without xen
o, x, x, 1, 1 (toggle xen off, and back on) boots xen
o, x, x, x, 1, 1 (toggle xen off, on, and back off), boots without xen

boot with xen_kernel not set: menu item says N/A
toggle xen option when N/A: no op

using menu item 5 to switch to kernel.old, with xen still active. loads xen then loads kernel.old as expected

[dteske]

We should probably include in the diff a bump to PORTREVISION in Makefile.

[dteske]

Add PORTREVISION bump in Makefile

[allanjude]

[bapt]

Can one upload the diff again so that I can look at it? recent changes on phabricator lost some diffs including that one :(

[dteske]

Reup the diff