file: Parse some UFS2 flags

This allows libmagic to recognize the FS_DOSOFTDEP, FS_SUJ, FS_GJOURNAL,
FS_ACLS, and FS_NFS4ACLS flags on a UFS2 file system.

Accepted upstream as 482259e5e952.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D56010