getdevpath.3: Fix reference and sort.

DEVTAB - Add mountroot & fstab support for serial numbers, and devtab.

* The vfs.root.mountfrom /boot/loader.conf variable may now specify
devfs aliases, allowing it to specify root mounts by seri

DEVTAB - Add mountroot & fstab support for serial numbers, and devtab.

* The vfs.root.mountfrom /boot/loader.conf variable may now specify
devfs aliases, allowing it to specify root mounts by serial number.
Here is an example:

vfs.root.mountfrom="hammer:serno/L41JYE0G.s1d"

Note that vfs.root.mountfrom may NOT currently specify /etc/devtab labels.

* /etc/fstab may now specify devfs relative paths (such as serial numbers)
as well as /etc/devtab labels. A ".suffix" may be used to extend the
translation so /etc/devtab only needs to specify the base label.

Example /etc/fstab:

# Device Mountpoint FStype Options Dump Pass
#
driveA.s1d / hammer rw 1 1
driveA.s1b none swap sw 0 0
driveA.s1a /boot ufs rw 1 1
serno/L41JYE0G.s1d /fubar hammer rw 1 1

/etc/devtab:

driveA serno L41JYE0G

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