[IPSEC]: Add XFRMA_SA/XFRMA_POLICY for delete notification

This patch changes the format of the XFRM_MSG_DELSA and
XFRM_MSG_DELPOLICY notification so that the main message
sent is of the same format as that received by the kernel
if the original message was via netlink.  This also means
that we won't lose the byid information carried in km_event.

Since this user interface is introduced by Jamal's patch
we can still afford to change it.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>