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

Commit b5f86218

 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 <suresh2514@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>