32 bits to 64 bits and eliminates the unused mnt_xflag field. The
existing mnt_flag field is completely out of bits, so this update
gives us room to expand. Note that the f_flags field in the statfs
structure is already 64 bits, so the expanded mnt_flag field can
be exported without having to make any changes in the statfs structure.
Approved by: re (bz)