Last slave down in bonding broadcast mode cause network unreachable

Issue

• In Linux bonding scenario, one packet is copied to several copies and sent by all slave device of bond0 in mode 3(broadcast mode). The mode 3 xmit function bond_xmit_broadcast() only ueses the last slave device's tx result as the final result. In this case, if the last slave device is down, then it always return NET_XMIT_DROP, even though the other slave devices xmit success. It may cause the tx statistics error, and cause the application (e.g. scp,iperf) consider the network is unreachable.