unfs3: Fix utime for symlink in attr.c

unfs3: Fix utime for symlink in attr.c

unfs3 has an old defect that it can not change the timestamps of a
symlink file because it only uses utime(), which will follow the
symlink. This will not cause an error if the symlink points to an
existent file but can be triggered with rpm workflows.

Making unfs3 support lutimes() addresses this problem.

(From OE-Core rev: 244a5be0eab31310b8717ab6b713c2902def4e0c)

Signed-off-by: Rui Wang <rui.wang@windriver.com>
Signed-off-by: Joe Slater <joe.slater@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>