Ensure that the mount command shows "with quotas" when quotas are enabled.

Ensure that the mount command shows "with quotas" when quotas are enabled.

When quotas are enabled with the quotaon(8) command, it sets the
MNT_QUOTA flag in the mount structure mnt_flag field. The mount
structure holds a cached copy of the filesystem statfs structure
in mnt_stat that includes a copy of the mnt_flag field in
mnt_stat.f_flags. The mnt_stat structure may not be updated for
hours. Since the mount command requests mount details using the
MNT_NOWAIT option, it gets the mount's mnt_stat statfs structure
whose f_flags field does not yet show the MNT_QUOTA flag being set
in mnt_flag.

The fix is to have quotaon(8) set the MNT_QUOTA flag in both mnt_flag
and in mnt_stat.f_flags so that it will be immediately visible to
callers of statfs(2).

Reported by:  Christos Chatzaras
Tested by:    Christos Chatzaras
PR:           254682
MFC after:    3 days
Sponsored by: Netflix