If switching RW->RO, then stop deferring timestamp writes...and possibly

If switching RW->RO, then stop deferring timestamp writes...and possibly
other pending inode attribute changes.  We appear to be missing UFS_UPDATE()
calls in some paths with the result that bsd.rd remounting the newly
created /mnt to RO would lose the GID changes on device inodes there.
This only affected devices, as they're the only inodes where timestamp
writes are delayed.

ok deraadt@