[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/ipv6/mcast.c b/net/ipv6/mcast.c
index 639eb20..3b114e3 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -171,7 +171,7 @@
 
 #define IPV6_MLD_MAX_MSF	64
 
-int sysctl_mld_max_msf = IPV6_MLD_MAX_MSF;
+int sysctl_mld_max_msf __read_mostly = IPV6_MLD_MAX_MSF;
 
 /*
  *	socket join on multicast group