mtree: Fix -f -f not considering type changes.

This only lists the changed type and not other attributes so that it
matches the behavior of -C as done in r66747 for fmtree. The NetBSD
-ff implementation was copied from fmtree.

Reviewed by: imp
MFC after: 2 weeks
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D21623