ipv4: Define __ipv4_neigh_lookup_noref when CONFIG_INET is disabled

mainline inclusion
from mainline-5.1
commit 9b3040a6
category: bugfix
bugzilla: 15168
CVE: NA

-------------------------------------------------

Define __ipv4_neigh_lookup_noref to return NULL when CONFIG_INET is disabled.

Fixes: 4b2a2bfe ("neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit")
Reported-by: Nkbuild test robot <lkp@intel.com>
Signed-off-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NZhiqiang Liu <liuzhiqiang26@huawei.com>
Reviewed-by: NWenan Mao <maowenan@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/net/arp.h

@@ -18,6 +18,7 @@ static inline u32 arp_hashfn(const void *pkey, const struct net_device *dev, u32
 	return val * hash_rnd[0];
 }
 
+#ifdef CONFIG_INET
 static inline struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
 {
 	if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
@@ -25,6 +26,13 @@ static inline struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev
 
 	return ___neigh_lookup_noref(&arp_tbl, neigh_key_eq32, arp_hashfn, &key, dev);
 }
+#else
+static inline
+struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
+{
+	return NULL;
+}
+#endif
 
 static inline struct neighbour *__ipv4_neigh_lookup(struct net_device *dev, u32 key)
 {