dp83640: Always decode received status frames

Currently status frames are only handled when packet timestamping is
enabled, but status frames are also needed for pin event timestamping.

Fix by moving packet timestamping check to after status frame decode.

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>