bonding: do not discard lowest hash bit for non layer3+4 hashing

Commit b5f8621 was introduced to discard lowest hash bit for layer3+4 hashing
but it also removes last bit from non layer3+4 hashing

Below script shows layer2+3 hashing will result in same slave to be used with above commit.
$ cat hash.py
#/usr/bin/python3.6

h_dests=[0xa0, 0xa1]
h_source=0xe3
hproto=0x8
saddr=0x1e7aa8c0
daddr=0x17aa8c0

for h_dest in h_dests:
    hash = (h_dest ^ h_source ^ hproto ^ saddr ^ daddr)
    hash ^= hash >> 16
    hash ^= hash >> 8
    print(hash)

print("with last bit removed")
for h_dest in h_dests:
    hash = (h_dest ^ h_source ^ hproto ^ saddr ^ daddr)
    hash ^= hash >> 16
    hash ^= hash >> 8
    hash = hash >> 1
    print(hash)

Output:
$ python3.6 hash.py
522133332
522133333   <-------------- will result in both slaves being used

with last bit removed
261066666
261066666   <-------------- only single slave used

Signed-off-by: suresh kumar <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: suresh2514

drivers/net/bonding/bond_main.c

@@ -4027,14 +4027,19 @@ static bool bond_flow_dissect(struct bonding *bond, struct sk_buff *skb, const v
 	return true;
 }
 
-static u32 bond_ip_hash(u32 hash, struct flow_keys *flow)
+static u32 bond_ip_hash(u32 hash, struct flow_keys *flow, int xmit_policy)
 {
 	hash ^= (__force u32)flow_get_u32_dst(flow) ^
 		(__force u32)flow_get_u32_src(flow);
 	hash ^= (hash >> 16);
 	hash ^= (hash >> 8);
+
 	/* discard lowest hash bit to deal with the common even ports pattern */
-	return hash >> 1;
+	if (xmit_policy == BOND_XMIT_POLICY_LAYER34 ||
+		xmit_policy == BOND_XMIT_POLICY_ENCAP34)
+		return hash >> 1;
+
+	return hash;
 }
 
 /* Generate hash based on xmit policy. If @skb is given it is used to linearize
@@ -4064,7 +4069,7 @@ static u32 __bond_xmit_hash(struct bonding *bond, struct sk_buff *skb, const voi
 			memcpy(&hash, &flow.ports.ports, sizeof(hash));
 	}
 
-	return bond_ip_hash(hash, &flow);
+	return bond_ip_hash(hash, &flow, bond->params.xmit_policy);
 }
 
 /**
@@ -5259,7 +5264,7 @@ static u32 bond_sk_hash_l34(struct sock *sk)
 	/* L4 */
 	memcpy(&hash, &flow.ports.ports, sizeof(hash));
 	/* L3 */
-	return bond_ip_hash(hash, &flow);
+	return bond_ip_hash(hash, &flow, BOND_XMIT_POLICY_LAYER34);
 }
 
 static struct net_device *__bond_sk_get_lower_dev(struct bonding *bond,