[NET/IPV4/IPV6]: Change some sysctl variables to __read_mostly

Change net/core, ipv4 and ipv6 sysctl variables to __read_mostly.

Couldn't actually measure any performance increase while testing (.3%
I consider noise), but seems like the right thing to do.

Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2973dee..23b46e3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -78,8 +78,8 @@
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 
-int sysctl_tcp_tw_reuse;
-int sysctl_tcp_low_latency;
+int sysctl_tcp_tw_reuse __read_mostly;
+int sysctl_tcp_low_latency __read_mostly;
 
 /* Check TCP sequence numbers in ICMP packets. */
 #define ICMP_MIN_LENGTH 8