bonding: Always assign be16 value to vlan_proto

The type of the vlan_proto field is __be16.
And most users of the field use it as such.

In the case of setting or testing the field for the special VLAN_N_VID
value, host byte order is used. Which seems incorrect.

It also seems somewhat odd to store a VLAN ID value in a field that is
otherwise used to store Ether types.

Address this issue by defining BOND_VLAN_PROTO_NONE, a big endian value.
0xffff was chosen somewhat arbitrarily. What is important is that it
doesn't overlap with any valid VLAN Ether types.

I don't believe the problems described above are a bug because
VLAN_N_VID in both little-endian and big-endian byte order does not
conflict with any supported VLAN Ether types in big-endian byte order.

Reported by sparse as:

 .../bond_main.c:2857:26: warning: restricted __be16 degrades to integer
 .../bond_main.c:2863:20: warning: restricted __be16 degrades to integer
 .../bond_main.c:2939:40: warning: incorrect type in assignment (different base types)
 .../bond_main.c:2939:40:    expected restricted __be16 [usertype] vlan_proto
 .../bond_main.c:2939:40:    got int

No functional changes intended.
Compile tested only.
Signed-off-by: Simon Horman <horms@kernel.org>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -2871,6 +2871,8 @@ static bool bond_has_this_ip(struct bonding *bond, __be32 ip)
 	return ret;
 }
 
+#define BOND_VLAN_PROTO_NONE cpu_to_be16(0xffff)
+
 static bool bond_handle_vlan(struct slave *slave, struct bond_vlan_tag *tags,
 			     struct sk_buff *skb)
 {
@@ -2878,13 +2880,13 @@ static bool bond_handle_vlan(struct slave *slave, struct bond_vlan_tag *tags,
 	struct net_device *slave_dev = slave->dev;
 	struct bond_vlan_tag *outer_tag = tags;
 
-	if (!tags || tags->vlan_proto == VLAN_N_VID)
+	if (!tags || tags->vlan_proto == BOND_VLAN_PROTO_NONE)
 		return true;
 
 	tags++;
 
 	/* Go through all the tags backwards and add them to the packet */
-	while (tags->vlan_proto != VLAN_N_VID) {
+	while (tags->vlan_proto != BOND_VLAN_PROTO_NONE) {
 		if (!tags->vlan_id) {
 			tags++;
 			continue;
@@ -2960,7 +2962,7 @@ struct bond_vlan_tag *bond_verify_device_path(struct net_device *start_dev,
 		tags = kcalloc(level + 1, sizeof(*tags), GFP_ATOMIC);
 		if (!tags)
 			return ERR_PTR(-ENOMEM);
-		tags[level].vlan_proto = VLAN_N_VID;
+		tags[level].vlan_proto = BOND_VLAN_PROTO_NONE;
 		return tags;
 	}