[NET]: use __read_mostly on kmem_cache_t , DEFINE_SNMP_STAT pointers

This patch puts mostly read only data in the right section
(read_mostly), to help sharing of these data between CPUS without
memory ping pongs.

On one of my production machine, tcp_statistics was sitting in a
heavily modified cache line, so *every* SNMP update had to force a
reload.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ipv6_sockglue.c

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 7516b88..76466af 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -55,7 +55,7 @@
 
 #include <asm/uaccess.h>
 
-DEFINE_SNMP_STAT(struct ipstats_mib, ipv6_statistics);
+DEFINE_SNMP_STAT(struct ipstats_mib, ipv6_statistics) __read_mostly;
 
 static struct packet_type ipv6_packet_type = {
 	.type = __constant_htons(ETH_P_IPV6),