headers/prep: Fix header to build standalone: <net/netfilter/ipv6/nf_defrag_ipv6.h>

Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/net/netfilter/ipv6/nf_defrag_ipv6.h

diff --git a/include/net/netfilter/ipv6/nf_defrag_ipv6.h b/include/net/netfilter/ipv6/nf_defrag_ipv6.h
index ceadf8b..9cc9abb 100644
--- a/include/net/netfilter/ipv6/nf_defrag_ipv6.h
+++ b/include/net/netfilter/ipv6/nf_defrag_ipv6.h
@@ -5,6 +5,8 @@
 #include <linux/skbuff.h>
 #include <linux/types.h>
 
+struct net;
+
 int nf_defrag_ipv6_enable(struct net *net);
 void nf_defrag_ipv6_disable(struct net *net);