[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/igmp.c b/net/ipv4/igmp.c
index 7003e76..58be822 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1397,8 +1397,8 @@
 /*
  *	Join a socket to a group
  */
-int sysctl_igmp_max_memberships = IP_MAX_MEMBERSHIPS;
-int sysctl_igmp_max_msf = IP_MAX_MSF;
+int sysctl_igmp_max_memberships __read_mostly = IP_MAX_MEMBERSHIPS;
+int sysctl_igmp_max_msf __read_mostly = IP_MAX_MSF;
 
 
 static int ip_mc_del1_src(struct ip_mc_list *pmc, int sfmode,