netns: introduce the net_hash_mix "salt" for hashes

There are many possible ways to add this "salt", thus I made this
patch to be the last in the series to change it if required.

Currently I propose to use the struct net pointer itself as this 
salt, but since this pointer is most often cache-line aligned, shift 
this right to eliminate the bits, that are most often zeroed.

After this, simply add this mix to prepared hashfn-s.

For CONFIG_NET_NS=n case this salt is 0 and no changes in hashfn
appear.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_sock.h

@@ -25,6 +25,7 @@
 #include <net/sock.h>
 #include <net/request_sock.h>
 #include <net/route.h>
+#include <net/netns/hash.h>
 
 /** struct ip_options - IP Options
  *
@@ -178,7 +179,7 @@ static inline unsigned int inet_ehashfn(struct net *net,
 	return jhash_3words((__force __u32) laddr,
 			    (__force __u32) faddr,
 			    ((__u32) lport) << 16 | (__force __u32)fport,
-			    inet_ehash_secret);
+			    inet_ehash_secret + net_hash_mix(net));
 }
 
 static inline int inet_sk_ehashfn(const struct sock *sk)