bonding: remove unwanted lock for bond enslave and release

The bond_change_active_slave() and bond_select_active_slave()
do't need bond lock anymore, so remove the unwanted bond lock
for these two functions.

The bond_select_active_slave() will release and acquire
curr_slave_lock, so the curr_slave_lock need to protect
the function.

In bond enslave and bond release, the bond slave list is also
protected by RTNL, so bond lock is no need to exist, remove
the lock and clean the functions.

Suggested-by: Jay Vosburgh <fubar@us.ibm.com>
Suggested-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>