net: bonding: remove unnecessary braces

Braces {} are not necessary for single statement blocks,
so remove these braces {}.

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>