net: bonding: fix error return code of bond_neigh_init()

When slave is NULL or slave_ops->ndo_neigh_setup is NULL, no error
return code of bond_neigh_init() is assigned.
To fix this bug, ret is assigned with -EINVAL in these cases.

Fixes: 9e99bfef ("bonding: fix bond_neigh_init()")
Reported-by: NTOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: NJia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -3978,11 +3978,15 @@ static int bond_neigh_init(struct neighbour *n)
 
 	rcu_read_lock();
 	slave = bond_first_slave_rcu(bond);
-	if (!slave)
+	if (!slave) {
+		ret = -EINVAL;
 		goto out;
+	}
 	slave_ops = slave->dev->netdev_ops;
-	if (!slave_ops->ndo_neigh_setup)
+	if (!slave_ops->ndo_neigh_setup) {
+		ret = -EINVAL;
 		goto out;
+	}
 
 	/* TODO: find another way [1] to implement this.
 	 * Passing a zeroed structure is fragile,