netfilter: bridge: fix CONFIG_NF_DEFRAG_IPV4/6 related warnings/errors

br_nf_ip_fragment() is not needed when neither CONFIG_NF_DEFRAG_IPV4 nor
CONFIG_NF_DEFRAG_IPV6 is set.

struct brnf_frag_data must be available if either CONFIG_NF_DEFRAG_IPV4
or CONFIG_NF_DEFRAG_IPV6 is set.

Fixes: efb6de9b ("netfilter: bridge: forward IPv6 fragmented packets")
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NBernhard Thaler <bernhard.thaler@wvnet.at>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/bridge/br_netfilter_hooks.c

@@ -111,7 +111,7 @@ static inline __be16 pppoe_proto(const struct sk_buff *skb)
 /* largest possible L2 header, see br_nf_dev_queue_xmit() */
 #define NF_BRIDGE_MAX_MAC_HEADER_LENGTH (PPPOE_SES_HLEN + ETH_HLEN)
 
-#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4) || IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
 struct brnf_frag_data {
 	char mac[NF_BRIDGE_MAX_MAC_HEADER_LENGTH];
 	u8 encap_size;
@@ -694,6 +694,7 @@ static int br_nf_push_frag_xmit(struct sock *sk, struct sk_buff *skb)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
 static int br_nf_ip_fragment(struct sock *sk, struct sk_buff *skb,
 			     int (*output)(struct sock *, struct sk_buff *))
 {
@@ -712,6 +713,7 @@ static int br_nf_ip_fragment(struct sock *sk, struct sk_buff *skb,
 
 	return ip_do_fragment(sk, skb, output);
 }
+#endif
 
 static unsigned int nf_bridge_mtu_reduction(const struct sk_buff *skb)
 {