netfilter: fix nf_conntrack_bridge/ipv6 link error

When CONFIG_IPV6 is disabled, the bridge netfilter code
produces a link error:

ERROR: "br_ip6_fragment" [net/bridge/netfilter/nf_conntrack_bridge.ko] undefined!
ERROR: "nf_ct_frag6_gather" [net/bridge/netfilter/nf_conntrack_bridge.ko] undefined!

The problem is that it assumes that whenever IPV6 is not a loadable
module, we can call the functions direction. This is clearly
not true when IPV6 is disabled.

There are two other functions defined like this in linux/netfilter_ipv6.h,
so change them all the same way.

Fixes: 764dd16 ("netfilter: nf_conntrack_bridge: add support for IPv6")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter_ipv6.h

@@ -75,8 +75,10 @@ static inline int nf_ipv6_chk_addr(struct net *net, const struct in6_addr *addr,
 		return 1;
 
 	return v6_ops->chk_addr(net, addr, dev, strict);
-#else
+#elif IS_BUILTIN(CONFIG_IPV6)
 	return ipv6_chk_addr(net, addr, dev, strict);
+#else
+	return 1;
 #endif
 }
 
@@ -113,8 +115,10 @@ static inline int nf_ipv6_br_defrag(struct net *net, struct sk_buff *skb,
 		return 1;
 
 	return v6_ops->br_defrag(net, skb, user);
-#else
+#elif IS_BUILTIN(CONFIG_IPV6)
 	return nf_ct_frag6_gather(net, skb, user);
+#else
+	return 1;
 #endif
 }
 
@@ -138,8 +142,10 @@ static inline int nf_br_ip6_fragment(struct net *net, struct sock *sk,
 		return 1;
 
 	return v6_ops->br_fragment(net, sk, skb, data, output);
-#else
+#elif IS_BUILTIN(CONFIG_IPV6)
 	return br_ip6_fragment(net, sk, skb, data, output);
+#else
+	return 1;
 #endif
 }
 
@@ -154,8 +160,10 @@ static inline int nf_ip6_route_me_harder(struct net *net, struct sk_buff *skb)
 		return -EHOSTUNREACH;
 
 	return v6_ops->route_me_harder(net, skb);
-#else
+#elif IS_BUILTIN(CONFIG_IPV6)
 	return ip6_route_me_harder(net, skb);
+#else
+	return -EHOSTUNREACH;
 #endif
 }