[IPSEC] Set byid for km_event in xfrm_get_policy

This patch fixes policy deletion in xfrm_user so that it sets
km_event.data.byid.  This puts xfrm_user on par with what af_key
does in this case.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

net/xfrm/xfrm_user.c

@@ -883,6 +883,7 @@ static int xfrm_get_policy(struct sk_buff *skb, struct nlmsghdr *nlh, void **xfr
 					      MSG_DONTWAIT);
 		}
 	} else {
+		c.data.byid = p->index;
 		c.event = XFRM_SAP_DELETED;
 		c.seq = nlh->nlmsg_seq;
 		c.pid = nlh->nlmsg_pid;