bond: check if slave count is 0 in case when deciding to take slave's mac

in bond_enslave(), check slave_cnt before actually using slave address.

introduced by:
commit 409cc1f8 (bond: have random dev address by default instead of zeroes)
Reported-by: NGreg Rose <gregory.v.rose@intel.com>
Signed-off-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -1629,7 +1629,7 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 
 	/* If this is the first slave, then we need to set the master's hardware
 	 * address to be the same as the slave's. */
-	if (bond->dev_addr_from_first)
+	if (bond->slave_cnt == 0 && bond->dev_addr_from_first)
 		bond_set_dev_addr(bond->dev, slave_dev);
 
 	new_slave = kzalloc(sizeof(struct slave), GFP_KERNEL);