netfilter: add and use nf_ct_set helper

Add a helper to assign a nf_conn entry and the ctinfo bits to an sk_buff.
This avoids changing code in followup patch that merges skb->nfct and
skb->nfctinfo into skb->_nfct.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index 4525579..d1fbfca 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -460,8 +460,7 @@
 
 	ct = nf_ct_tuplehash_to_ctrack(h);
 
-	skb->nfct = &ct->ct_general;
-	skb->nfctinfo = ovs_ct_get_info(h);
+	nf_ct_set(skb, ct, ovs_ct_get_info(h));
 	return ct;
 }
 
@@ -724,8 +723,7 @@
 			if (skb_nfct(skb))
 				nf_conntrack_put(skb_nfct(skb));
 			nf_conntrack_get(&tmpl->ct_general);
-			skb->nfct = &tmpl->ct_general;
-			skb->nfctinfo = IP_CT_NEW;
+			nf_ct_set(skb, tmpl, IP_CT_NEW);
 		}
 
 		err = nf_conntrack_in(net, info->family,