icmp: allow icmpv6_ndo_send to work with CONFIG_IPV6=n

The icmpv6_send function has long had a static inline implementation
with an empty body for CONFIG_IPV6=n, so that code calling it doesn't
need to be ifdef'd. The new icmpv6_ndo_send function, which is intended
for drivers as a drop-in replacement with an identical function
signature, should follow the same pattern. Without this patch, drivers
that used to work with CONFIG_IPV6=n now result in a linker error.

Cc: Chen Zhou <chenzhou10@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 0b41713b ("icmp: introduce helper for nat'd source address in network device context")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/icmpv6.h

@@ -22,19 +22,23 @@ extern int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn);
 int ip6_err_gen_icmpv6_unreach(struct sk_buff *skb, int nhs, int type,
 			       unsigned int data_len);
 
+#if IS_ENABLED(CONFIG_NF_NAT)
+void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info);
+#else
+#define icmpv6_ndo_send icmpv6_send
+#endif
+
 #else
 
 static inline void icmpv6_send(struct sk_buff *skb,
 			       u8 type, u8 code, __u32 info)
 {
-
 }
-#endif
 
-#if IS_ENABLED(CONFIG_NF_NAT)
-void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info);
-#else
-#define icmpv6_ndo_send icmpv6_send
+static inline void icmpv6_ndo_send(struct sk_buff *skb,
+				   u8 type, u8 code, __u32 info)
+{
+}
 #endif
 
 extern int				icmpv6_init(void);