[DECNET] address: Convert to new netlink interface

Extends the netlink interface to support the __le16 type and
converts address addition, deletion and, dumping to use the
new netlink interface.

Fixes multiple occasions of possible illegal memory references
due to not validated netlink attributes.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>