netfilter: conntrack: use siphash_4u64

This function is used for every packet, siphash_4u64 is noticeably faster
than using local buffer + siphash:

Before:
  1.23%  kpktgend_0       [kernel.vmlinux]     [k] __siphash_unaligned
  0.14%  kpktgend_0       [nf_conntrack]       [k] hash_conntrack_raw
After:
  0.79%  kpktgend_0       [kernel.vmlinux]     [k] siphash_4u64
  0.15%  kpktgend_0       [nf_conntrack]       [k] hash_conntrack_raw

In the pktgen test this gives about ~2.4% performance improvement.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_core.c

@@ -211,28 +211,24 @@ static u32 hash_conntrack_raw(const struct nf_conntrack_tuple *tuple,
 			      unsigned int zoneid,
 			      const struct net *net)
 {
-	struct {
-		struct nf_conntrack_man src;
-		union nf_inet_addr dst_addr;
-		unsigned int zone;
-		u32 net_mix;
-		u16 dport;
-		u16 proto;
-	} __aligned(SIPHASH_ALIGNMENT) combined;
+	u64 a, b, c, d;
 
 	get_random_once(&nf_conntrack_hash_rnd, sizeof(nf_conntrack_hash_rnd));
 
-	memset(&combined, 0, sizeof(combined));
+	/* The direction must be ignored, handle usable tuplehash members manually */
+	a = (u64)tuple->src.u3.all[0] << 32 | tuple->src.u3.all[3];
+	b = (u64)tuple->dst.u3.all[0] << 32 | tuple->dst.u3.all[3];
 
-	/* The direction must be ignored, so handle usable members manually. */
-	combined.src = tuple->src;
-	combined.dst_addr = tuple->dst.u3;
-	combined.zone = zoneid;
-	combined.net_mix = net_hash_mix(net);
-	combined.dport = (__force __u16)tuple->dst.u.all;
-	combined.proto = tuple->dst.protonum;
+	c = (__force u64)tuple->src.u.all << 32 | (__force u64)tuple->dst.u.all << 16;
+	c |= tuple->dst.protonum;
 
-	return (u32)siphash(&combined, sizeof(combined), &nf_conntrack_hash_rnd);
+	d = (u64)zoneid << 32 | net_hash_mix(net);
+
+	/* IPv4: u3.all[1,2,3] == 0 */
+	c ^= (u64)tuple->src.u3.all[1] << 32 | tuple->src.u3.all[2];
+	d += (u64)tuple->dst.u3.all[1] << 32 | tuple->dst.u3.all[2];
+
+	return (u32)siphash_4u64(a, b, c, d, &nf_conntrack_hash_rnd);
 }
 
 static u32 scale_hash(u32 hash)