bonding: return -ENOMEM instead of BUG in alb_upper_dev_walk

If failed to allocate "tags" or could not find the final upper device from
start_dev's upper list in bond_verify_device_path(), only the loopback
detection of the current upper device should be affected, and the system is
no need to be panic.
So return -ENOMEM in alb_upper_dev_walk to stop walking, print some warn
information when failed to allocate memory for vlan tags in
bond_verify_device_path.

I also think that the following function calls
netdev_walk_all_upper_dev_rcu
---->>>alb_upper_dev_walk
---------->>>bond_verify_device_path
From this way, "end device" can eventually be obtained from "start device"
in bond_verify_device_path, IS_ERR(tags) could be instead of
IS_ERR_OR_NULL(tags) in alb_upper_dev_walk.

Signed-off-by: Zhengchao Shao <[e-mail]>
Acked-by: Jay Vosburgh <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/net/bonding/bond_alb.c

···
 	if (netif_is_macvlan(upper) && !strict_match) {
 		tags = bond_verify_device_path(bond->dev, upper, 0);
 		if (IS_ERR_OR_NULL(tags))
-			BUG();
+			return -ENOMEM;
+
 		alb_send_lp_vid(slave, upper->dev_addr,
 				tags[0].vlan_proto, tags[0].vlan_id);
 		kfree(tags);

drivers/net/bonding/bond_main.c

···
 
 	if (start_dev == end_dev) {
 		tags = kcalloc(level + 1, sizeof(*tags), GFP_ATOMIC);
-		if (!tags)
+		if (!tags) {
+			net_err_ratelimited("%s: %s: Failed to allocate tags\n",
+					    __func__, start_dev->name);
 			return ERR_PTR(-ENOMEM);
+		}
 		tags[level].vlan_proto = BOND_VLAN_PROTO_NONE;
 		return tags;
 	}