[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>
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index 4410b9d..f84ba9c 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -73,7 +73,7 @@
 /* Exported for inet_getid inline function.  */
 DEFINE_SPINLOCK(inet_peer_idlock);
 
-static kmem_cache_t *peer_cachep;
+static kmem_cache_t *peer_cachep __read_mostly;
 
 #define node_height(x) x->avl_height
 static struct inet_peer peer_fake_node = {