bonding: allow use of tx hashing in balance-alb

The rx load balancing provided by balance-alb is not mutually
exclusive with using hashing for tx selection, and should provide a decent
speed increase because this eliminates spinlocks and cache contention.

Signed-off-by: Debabrata Banerjee <dbanerje@akamai.com>
Signed-off-by: David S. Miller <davem@davemloft.net>