bonding: modify bond_get_slave_by_dev() to use neighbours

It should be used under rtnl/bonding lock, so use the non-RCU version.

CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>