- By default, use disklabels in the native endian.
- With options BSDDISKLABEL_EI, kernels can read/write labels
in the opposite endian.
- With options COMPAT_MMEYE_OLDLABEL, kernels accept labels
in format used on old mmeyes.
(Some old mmeyes have "the bootstrap kernel to load kernel from disks"
on their flash ROMs and it is not easy to update kernels on the ROMs.)
- While here, use leXXtoh() to read some values in MBR.
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