[NETNS][IPV6]: Make ipv6_sysctl_register to return a value.

This patch makes the function ipv6_sysctl_register to return a
value. The af_inet6 init function is now able to handle an error and
catch it from the initialization of the sysctl.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index 4ad8d9d..f713fbf 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -91,10 +91,15 @@
 
 static struct ctl_table_header *ipv6_sysctl_header;
 
-void ipv6_sysctl_register(void)
+int ipv6_sysctl_register(void)
 {
 	ipv6_sysctl_header = register_sysctl_paths(net_ipv6_ctl_path,
-			ipv6_table);
+						   ipv6_table);
+	if (!ipv6_sysctl_header)
+		return -ENOMEM;
+
+	return 0;
+
 }
 
 void ipv6_sysctl_unregister(void)