bonding: slight optimizztion for bond_slave_override()

When the skb is xmit by the function bond_slave_override(),
it will have duplicate judgement for slave state, and I think it
will consumes a little performance, maybe it is negligible,
so I simplify the function and remove the unwanted judgement.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>