[NET] sysctl: prepare core tables to point to netns variables

Some of ctl variables are going to be on the struct
net. Here's the way to adjust the ->data pointer on the
ctl_table-s to point on the right variable.

Since some pointers still point on the global variables,
I keep turning the write bits off on such tables.

This looks to become a common procedure for net sysctls,
so later parts of this code may migrate to some more
generic place.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/sysctl_net_core.c

@@ -167,8 +167,13 @@ static __net_init int sysctl_core_net_init(struct net *net)
 		if (tbl == NULL)
 			goto err_dup;
 
-		for (tmp = tbl; tmp->procname; tmp++)
-			tmp->mode &= ~0222;
+		for (tmp = tbl; tmp->procname; tmp++) {
+			if (tmp->data >= (void *)&init_net &&
+					tmp->data < (void *)(&init_net + 1))
+				tmp->data += (char *)net - (char *)&init_net;
+			else
+				tmp->mode &= ~0222;
+		}
 	}
 
 	net->sysctl_core_hdr = register_net_sysctl_table(net,