netfilter: nf_conntrack: split up IPCT_STATUS event

Split up the IPCT_STATUS event into an IPCT_REPLY event, which is generated
when the IPS_SEEN_REPLY bit is set, and an IPCT_ASSURED event, which is
generated when the IPS_ASSURED bit is set.

In combination with a following patch to support selective event delivery,
this can be used for "sparse" conntrack replication: start replicating the
conntrack entry after it reached the ASSURED state and that way it's SYN-flood
resistant.

Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 16f86d6..ff594eb 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -1371,7 +1371,8 @@
 			else
 				events = IPCT_NEW;
 
-			nf_conntrack_eventmask_report((1 << IPCT_STATUS) |
+			nf_conntrack_eventmask_report((1 << IPCT_REPLY) |
+						      (1 << IPCT_ASSURED) |
 						      (1 << IPCT_HELPER) |
 						      (1 << IPCT_PROTOINFO) |
 						      (1 << IPCT_NATSEQADJ) |
@@ -1396,7 +1397,8 @@
 		if (err == 0) {
 			nf_conntrack_get(&ct->ct_general);
 			spin_unlock_bh(&nf_conntrack_lock);
-			nf_conntrack_eventmask_report((1 << IPCT_STATUS) |
+			nf_conntrack_eventmask_report((1 << IPCT_REPLY) |
+						      (1 << IPCT_ASSURED) |
 						      (1 << IPCT_HELPER) |
 						      (1 << IPCT_PROTOINFO) |
 						      (1 << IPCT_NATSEQADJ) |