af_key: more info leaks in pfkey messages

This is inspired by a5cc68f3 "af_key: fix info leaks in notify
messages".  There are some struct members which don't get initialized
and could disclose small amounts of private information.

Acked-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>