bonding: bond_slave_info_query() fix

bond_slave_info_query() should keep a read lock while accessing slave info,
or risk accessing stale data and corruption.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>