Every time I do a VM2VM iperf test with vhost example, I have to set the arp table manually, as vhost-switch just ignores the broadcast packet, leaving the ARP request not served. Here we do a transmit a broadcast packet (such as ARP request) to every vhost device, as well as the physical port, to fix above arp table issue. Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>