netfilter: decnet: switch hook PFs to nfproto

This patch is a cleanup. Use NFPROTO_* for consistency with other
netfilter code.

Signed-off-by: Alban Crequy <alban.crequy@collabora.co.uk>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Vincent Sanders <vincent.sanders@collabora.co.uk>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/decnet/netfilter/dn_rtmsg.c

@@ -117,7 +117,7 @@ static inline void dnrmg_receive_user_skb(struct sk_buff *skb)
 
 static struct nf_hook_ops dnrmg_ops __read_mostly = {
 	.hook		= dnrmg_hook,
-	.pf		= PF_DECnet,
+	.pf		= NFPROTO_DECNET,
 	.hooknum	= NF_DN_ROUTE,
 	.priority	= NF_DN_PRI_DNRTMSG,
 };