[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/dccp/ccids/ccid3.c

@@ -85,7 +85,7 @@ static int ccid3_debug;
 static struct dccp_tx_hist *ccid3_tx_hist;
 static struct dccp_rx_hist *ccid3_rx_hist;
 
-static kmem_cache_t *ccid3_loss_interval_hist_slab;
+static kmem_cache_t *ccid3_loss_interval_hist_slab __read_mostly;
 
 static inline struct ccid3_loss_interval_hist_entry *
 	ccid3_loss_interval_hist_entry_new(const unsigned int __nocast prio)