bonding: remove unwanted lock for bond_store_primaryxxx()

The bond_select_active_slave() will not release and acquire
bond lock, so it is no need to read the bond lock for them,
and the bond_store_primaryxxx() is already in RTNL, so remove the
unwanted lock.

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>