MFC r285885 by brueffer:

In tmpfs_chtimes(), remove checks on the nanosecond level when
determining whether a node changed.

Other filesystems, e.g., UFS, only check on seconds, when determining
whether something changed.

This also corrects the birthtime case, where we checked tv_nsec
twice, instead of tv_sec and tv_nsec (PR).

PR: 201284