fusefs: clear a dir's attr cache when its contents change

Any change to a directory's contents should cause its mtime and ctime to be
updated by the FUSE daemon. Clear its attribute cache so we'll get the new
attributs the next time that they're needed. This affects the following
VOPs: VOP_CREATE, VOP_LINK, VOP_MKDIR, VOP_MKNOD, VOP_REMOVE, VOP_RMDIR, and
VOP_SYMLINK

Reported by: pjdfstest
Sponsored by: The FreeBSD Foundation