ipv6: coding style: comparison for equality with NULL

The ipv6 code uses a mixture of coding styles. In some instances check for NULL
pointer is done as x == NULL and sometimes as !x. !x is preferred according to
checkpatch and this patch makes the code consistent by adopting the latter
form.

No changes detected by objdiff.

Signed-off-by: Ian Morris <ipm@chirality.org.uk>
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 30f5a4a..abcc79f 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -179,7 +179,7 @@
 	int err = -ENOMEM;
 
 	ip6_header = register_net_sysctl(&init_net, "net/ipv6", ipv6_rotable);
-	if (ip6_header == NULL)
+	if (!ip6_header)
 		goto out;
 
 	err = register_pernet_subsys(&ipv6_sysctl_net_ops);