[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/dccp/proto.c b/net/dccp/proto.c
index 600dda5..f97e92e 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -39,7 +39,7 @@
 #include "ccid.h"
 #include "dccp.h"
 
-DEFINE_SNMP_STAT(struct dccp_mib, dccp_statistics);
+DEFINE_SNMP_STAT(struct dccp_mib, dccp_statistics) __read_mostly;
 
 atomic_t dccp_orphan_count = ATOMIC_INIT(0);