FBSD: Accommodate 12.0's 64-bit inodes

FBSD: Accommodate 12.0's 64-bit inodes

In FreeBSD 12 (see: https://reviews.freebsd.org/rS318736), the layout
of struct dirent changed to allow for 64-bit inodes and a few other
changes. Update our struct min_direct to accommodate, to allow our
readdir() results to be accurate. Without this, readdir() can yield
garbage entries, due to the mismatch in the structure definitions.

Change-Id: I36c2bf1f35b4d1ab61a2b4d51da7514827b3551b
Reviewed-on: https://gerrit.openafs.org/13854
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>