netfilter: ipv6: use NFPROTO values for NF_HOOK invocation

The semantic patch that was used:
// <smpl>
@@
@@
(NF_HOOK
|NF_HOOK_THRESH
|nf_hook
)(
-PF_INET6,
+NFPROTO_IPV6,
 ...)
// </smpl>

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 52e0f74..430372e 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1566,7 +1566,7 @@
 
 	IP6CB(skb)->flags |= IP6SKB_FORWARDED;
 
-	return NF_HOOK(PF_INET6, NF_INET_FORWARD, skb, skb->dev, dev,
+	return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD, skb, skb->dev, dev,
 		       ip6mr_forward2_finish);
 
 out_free: